All good questions. There really isn't a progression of "what should I upgrade first, then second, etc", contrary to what some believe. It all depends on your uses for it and your budget, and those could easily change very fast between now and whenever you do get an upgrade.
They aren't, really. They only perform worse and have much louder noises. If OP can live with that and it's not negatively affecting his/her build, then I don't see much of a reason to upgrade.
Mostly just higher FPS, I get good FPS, but not great when recording. I also feel like it doesn't cool very well when running hardware intensive games. My price limit is around $200 as of now, but I can get more if need be.