I guess we all agree on one point: Ali should return either on a new movie, or in the TV series, so that the promess is kept.
English is a very tricky language, the usage of the word love can have all kinds of meanings, and not the only one of romance. Now, as kids grow up they usually pair out with other people and call them their girlfriend or boyfriend even if there is nothing remotely similar to love, and Littlefoot and Ali, are kids, as much as I prefer to see them as mature characters the series has taken its turn to make them more childish, for that in my opinion there has been a slight decrease in quality since lbt 4. I would be opened for a relationship between Ali and Littlefoot, it existing would be just a more tight friendship than the one Littlefoot experiences with the rest of the gang and nothing more. I agree with Littlefoot1616, there would be some sort of unbalance in the equilibrium created amongst the gang, but still I'd love it if Ali could stay in the great valley or become a more often guest star, I can't see any wrong coming out of it.
As for LBT 4, I do agree with Malte that it makes no sense for a herd to come to the great valley and leave in a couple of days, expecially after a long journey, they probably rested for at least a week, and I do believe that is enough time to form a ever lasting relationship (take it as friendship =p).
As for Grandpa and Grandma Longneck being the "leaders" of the valley, we'll I've been studying a bit of psychology, and I've just finished a work about the accomplishments of late life. We might take it for granted, but most of the world leaders were and are people of over 60 years old. Grandma and Granpa are clearly the most elderly dinosaurs in the valley, and seem very experienced and wise, so it's only natural the others will listen to them and seem themas some sort of guidance counselers (not sure on the spelling =x).
I have a theory about the how they're going to take Chomper off that island. If you remember LBT 5, Chomper says that there isn't much food on the island, so him and his parents have no reason to stay. Furthermore, I guess that land strip that helped the gang to reach the island isn't permantly gone, it's just probably underwater for a period of time due to a rise in the tides, and maybe it only shows up a few months a year, and when it reappears Chomper and his parents will seize their chance. I also believe that Chomper knows the way back to the great valley, he was born there, and came from there to the island, he might not know how to get in, but he and his parents surely know where it is.
Another theory is that we must look at the big picture. Through out the lbt's from 4 to 11, we have witnessed weird phenomenons, there is something happening to the planet, maybe the final extinction of the dinosaurs? I don't know where they are going with that, but it could make a very interesting ending for the land before time series, the gang, all the fokes in the great valley and all the dino's they met over the years, coming together to find the last safe haven on earth, maybe they would have to move out of the valley for survival, or maybe that safe haven is the valley, something around this, to finish what they were trying to start with the first movie. For a planet that was overgoing some tough changes they seemed to find many green areas out-side the valley, what if that is changing? I hope they try to make something out of this, make it a more mature plot and find a suitable ending for the series, I really can't see the lbt lasting forever, 11 movies is more than enough, and maybe the only thing that's keeping them together, their D. Sebastian (look up on portuguese history to get where I'm going with this =p) is the return of Ali.