Should I get Pathfinder?

[Bovine Colonel]

What I'm asking here is whether or not there are enough differences between D&D 3.5 and Pathfinder to make it worth getting PF, or any other reason why I should (or shouldn't) get PF.

There's not quite that much difference between the two. Pathfinder is certainly an improvement in at least some respects, but if you've already got books for 3.5 I suggest you stick with 3.5. Incidentally, you can find pretty much everything published for Pathfinder at http://www.d20pfsrd.com/

I too am curious about Pathfinder. Are classes that are yet to be remade in PF backward compatable, like 3e is to 3.5?

3.5 classes are generally considered compatible with Pathfinder. Some things (class skills, HD and BAB correlation, etc) may need changing but game balance isn't really affected.