Yes, as long as a tier is not limited and gone you can always upgrade (or downgrade) before the end.Can you upgrade tiers later? I know I at least want to go in for the $100 tier, but I might want to go all the way up to $300 for the signed box.
I don't really see how the character rendering (which is what people like about it most) depends in any way on the size of the stages.I wasn't there, but a friend of mine who attended the tech panel for Xrd at GDC told me that they said their engine wouldn't really work very well with a big Action/Adventure game or RPG. I'm guessing the reason why it looks so good is that they're only dealing with small stages and 2 characters at a time.
Exactly.Whatever budget this game winds up with will probably be too low to compete on a pixel art level with the best-looking 2D games. They'll get the best results for their budget with polygons.