There really is some serious potential in that kind of alternate scenario. That would be a way to widen the world while more easily keeping some of Bluth's original tone present unless the director just decided to forget the fact that the world was "dying". However, at this point it's difficult to say whether the series were "better". Had Universal gone the other path with the series, there might be a chance that LBT would have ended far earlier. Of course, quality is more important than quantity but still it's hard to predict this kind of change's impact into the series.
Like, if - for instance - they discovered that the mysterious "Great Valley" was not a place, but rather an allegory for a peaceful community of different species of flat-toothed dinosaurs living together.
I'd say it's safe to say this wouldn't happen. If the main characters found their families without finding the Valley, it's probable that the Gang would be forced to join their own separate herds as was implied in the fifth film. I don't think it's possible that all of the herds would be able to live together for long in the Mysterious Beyond.
Of course, if the Gang never finds their families, things are far different. In that case things become complicated and I'd say there's some very nice possibilities here. In that case, Universal would have to come up with some very nice plots in order to avoid repetition but it could work.
I'm not saying I'd like to see the Great Valley and the films being written off but there's a clear possibility that the franchise would have turned for the better in this scenario.
