A whole section of the forum dedicated to character sheets would, in my opinion, be a waste. Most roleplays generally take place in a completely different world to the rest, requiring extra/other criteria not found in other RPs, so it would be impossible or atleast very difficult to have one or even a handful of characters that could fit in the numerous worlds. IMO it's best to create a new character from scratch for each RP that you join, keeps things reasonably fresh and lets you explore new ideas. On that note, the "space saving" idea would probably have the opposite effect, creating a huge archive of characters that are only used once.

The battle idea I like, although it could get out of hand without moderation, a few restrictions would probably have to be set. I think it would be great if you could use already created characters from different RPs to battle eachother, with each one bringing parts of their own world with them (also adding permalinks of the character sheets, as they're often buried within OOC threads).

But hey, that's just me.