The only real sign of affection Bron ever shows to Shorty is when he lifts him upon his head near the end of the movie.
I don't consider that statement or the quote as proof positive of Bron's neglect. I haven't watched the movie recently, but from the way it sounded, Bron was talking in past tense, not present tense, so I keep thinking that Bron was only referring to what happened not long before his herd formed, not very recent events. There's no evidence to prove, or disprove it in my opinion, but Bron may have adopted Shorty before Littlefoot came.
Now someone might ask that, if he was adopted, why doesn't he stay close to Bron. Simple answer: the herd itself. The size of the herd makes it very safe for youngsters to wander around. As Bron said, sharpteeth won't attack a herd that size. So Shorty is safe with and without Bron as long as he stays close to the herd.
Also we must remember just what species these creatures are. They are sauropods. Watching a documentary I learned that the scientific theory about sauropods is that they lay their eggs and then leave them to fend for themselves. Young sauropods are capable of taking care of themselves if need be. This is proven in Littlefoot's case when he survives without his mother during the journey to the Great Valley.
But then, why did Littlefoot's mother stay behind to take care of him? Another simple answer: she wanted to protect "the next generation" so the species will survive. It's an instinct that all animals have, I think, and it may have caused a change in behavior and had the sauropods look after their young rather than abandon them like their kind usually would.
There is another special exception in the "normal sauropod behavior" and that's with Ali's herd. Since they migrated so much, if they laid an egg and it hatched, the herd would be long gone by then. But it is indicated that the herd lived inside the valley itself all these years, and migrated to different parts. They could have easily come back and let Ali join the herd.
Also Ali said that she spent much of her life socializing with just other longnecks. If she was left with other eggs and had siblings or playmates, then yes this would be true. Ali's timid behavior could derive from how young sauropods might have lived; hiding from fear, being very cautious around creatures they don't know.
So what I am pointing out is that, if Bron didn't adopt Shorty, it wasn't a bad thing. It wasn't like they were out in the Mysterious Beyond, all scattered into tiny groups, giving the sharpteeth the opportunity to attack. No, they were living in a small valley in a huge herd. Shorty could live just fine both on his own and with the direct care of Bron. After all he is a tough kid.
As for tracks on rocky ground, if we adopted the rules of LBT 10 to the oringinal movie it would be possible. Cera, Ducky, Petrie, and Spike seemed to be able not to loose the track of Littlefoot and his grandparents on rocky ground (and not even in a swamp).
This doesn't mean that Bron could have followed them. We must not forget weather, which can wash away the tracks, depending on the severity of the weather, or at least hide them. And if Bron were in his state of depression, he might have forgotten to follow the footprints, or even forgotten the significance they might have held.
To reply to your earlier statement on that, if Bron really was determined to find his son, he should've snapped himself back to reality and forced himself to move on, to keep trying. Now this seems like a logical idea. However, we must still remember Bron's tattered state of mind. Not able to think straight, making mistakes, etc.
Also, here's something to consider: Bron just might have stumbled upon his wife's body. There's no reason to suggest that he didn't. Seeing her like that would have worsened his state. This alone may have caused Bron to lose hope of ever finding his son, and thus this may have been the final straw that left his spirit broken, and no longer able to naturally know where the Great Valley was.
He would then blindly walk on, looking for Littlefoot, but always walking in one direction. His spirit is broken, and when someone's spirit is broken, it can take a long time to recover. Bron would try to hold on to some hope he'd find his son, but perhaps he would come upon a body that he thinks is Littlefoot, and is convinced his son is dead.
When he comes upon the small herd of baby longnecks, some glimmer of hope is renewed. Maybe one of them is his son. Alas this isn't so, and Bron may lose that hope again. I'm sure Bron's hope is somewhat renewed sometime after the formation of the herd. Perhaps Shorty is the one that renews Bron's hope.
But then why didn't he leave to the valley? Well maybe the loss of his ability to find the valley was permanent, and no matter how hard he tried, he just couldn't remember. Maybe one of the others could have lead him. Perhaps, but that doesn't directly mean that they would leave to the Great Valley. They were quite content on staying in the tiny valley where sharpteeth don't dare attack.
The longnecks seem to be quite cowardly too. Look at how they behaved when the sharpteeth attacked. They were paranoid to leave the safety of the valley, not even to help the little ones. Of the herd, only Bron was brave enough to leave and fight off the meat-eaters. So Bron isn't afraid to leave the walls of the tiny valley, but even if Bron had planned on going to the Great Valley, his biggest task would be to get the herd to come out.
He may be leader, but trying to get many cowardly longnecks to move outside the valley, despite how little of a chance there was to being attacked by sharpteeth, may be an obstacle that Bron couldn't overcome when he tried in the past. He also couldn't just leave them; they had appointed him leader, and as leader it was his responsibility to look after them, whether he wanted the position or not.
His message to Littlefoot about "dragging his herd to the Great Valley" is another indicator that getting the herd to leave will be quite a challenge. But Bron seems to be willing to try again. Whether or not it will be successful, no one can be too sure. But perhaps a later movie or an episode will verify if it does work.
Perhaps Bron never ever allowed himself to show any real affection feeling that by doing so he might either give up his son or else "betray his memory".
Hmm...I don't agree with this. I don't see why Bron would think showing affection towards someone else would be betrayal. I mean I show affection to other dogs, but my dog doesn't feel betrayed. People show affection towards a variety of things, not just a single few.
So Bron should not feel like he is betraying anyone just by showing affection towards Shorty or the other young longnecks. And he is certainly not giving up his son. I mean, if I had a kid, and lost the kid, maybe the kid ran away, and I gave affection to another kid, I am not giving up the first child at all. I am rather trying to ease my pain instead.
Now if Bron is faced with the same situation, then him showing affection to Shorty would help ease his pain, not make him give up or betray Littlefoot. But this showing affection would probably only surface after Bron has found the courage to move on, and break free of his depression, for the most part.
Knowledge of the Great Valley seems to have been very far spread by the time of the original movie; at least it is according to the claim of Littlefoot's mother that it was where all herds where heading.
Yes far spread, but that no way says that all or most of the dinosaurs knew the location. And taking what Action9000 had stated earlier, if Bron had went the opposite way, he would have indeed ended up in the wrong place. Now one can say he can ask for directions, but what if the directions were always the same? "Follow the bright circle to where it touches the ground." Now LBT10, as you say, suggests that footprints are easy to find. But does this mean Bron could have found them? No, not a chance.
Let's not forget that the Mysterious Beyond, the world, is huge. There is little chance of Bron being able to find the right set of tracks, leading in the right area. If he didn't meet up with a herd, and only knew the "follow the bright circle", he might have chosen to follow foosteps, if he found any, that lead in the wrong direction because he may have believed he should follow the morning sun and not the evening sun.
If Bron had truly believed this, that he was going the right way, he would probably not believe any dinosaur with the right directions, and perhaps tell them that they are the ones who are wrong. Bron would realize his mistake too late, but when I'm not sure. Perhaps after he reaches the small valley.
he flashback itself shows little of some energy the other dinosaurs apparently felt
One must understand that you cannot see energy, let alone see it happen. The flashback doesn't show everything, in fact it shows only a tiny tiny fraction of what actually happened.
The closest thing to see energy in progress is to watch a pack of dogs, especially a newcomer dog being introduced. One with an untrained eye won't see anything, but an expert dog handler would be most likely to notice how the energy from the calm dogs affects the behavior of the newcomer dog. The same process could have worked in the cause of the sauropods.
Surely there must have been something that made others look up to Bron.
The energy is one of the ways this might have occurred. Another is if Bron told them what he been through. If Bron had told the others about how he lost his wife and may have lost his son, but continued to search the Mysterious Beyond, still having some hope of finding his son, then taking in a little ground of longnecks, despite the state of mind he was in, facing the perils of the Mysterious Beyond all alone, all this may have helped the herd consider him a leader, and a role model to look up to.