The Land Before Time movies still have a lot of potential - in my opinion, it just depends on whether they decide to use it or not. Outwardly it does seem like they've milked the plots for all they're worth. After all, it's not easy coming up with conflict in the LBT world (at least not conflict that hasn't been used over and over.) You're basic antagonists are sharpteeth and natural disasters, and we see these in almost every movie. The question is, how do you liven things up? XD It's another reason why I have respect for the 7th movie - they decided to use a family member of one of the Gang as an actual villain. All the other "villains" were out for food. Back to the point, though - I wouldn't mind if they reintroduced certain characters like Doc, or Ally. Yeah I know we saw them in the episodes, but a movie would have been better...

They'd have received more screen time, and been involved in a deeper plot, which would have been interesting.
Other than that, they might have to stretch things and give human attributes to the dinosaurs (I mean more so than they already have) to keep things interesting. They could introduce a new villain who - like Pterano - isn't a bad guy because he/she is hungry and following instinct, but who actually has ulterior motives of some kind. Without, of course, making it resemble the 7th movie too closely.
It might come down to this question: What haven't we already seen that isn't redundant and also doesn't drift outside of the Land Before Time world too much?
XD