If you look at the submissions, I believe you'll find TONS of +5, and even a lot of +7.
*EDIT* I went through and counted. There are 41 cards of +7 or higher just in January's submissions. That's almost a full-sized set. If you lower it even to +5, that'd probably be bigger than any set ever released.
Pretty much any card can be guaranteed at least a few + since people like Sadness just upvote every single card. Having a cap at +5 or +7 will make people much more likely to play, because that's a fair guarantee the new cards aren't rubbish.
