"That probably all depends on if your scores will carry over to RB 2, which I sure as hell hope they do."I was just about to bring that up. I'm kind of hoping they don't forget about this, but it won't be such a big deal in the end (only care for a few DLC scores I like to keep track of).
As for the characters, it's OK either way, really. Since your characters can now play all instruments, there may be issues there.
The biggest problem with this would be the fact that Rock Band 1 will still need its character data. The new costumes and such from Rock Band 2 will overwrite the original ones, so it wouldn't make much sense to let the game be able to take those characters and write back and forth like that. There are obvious workarounds, sure, but... I'm not convinced it's worth their effort in the end.