I would pay too, but not too much, because there really isn't a lot to the game.. It's simple, like most arcade style games were back in the day. It's like a modern arcade game. It's fun and addictive, and all that, but it just doesn't have the depth of something like, even Stepmania. Stepmania allows each author to tailor their simfile to how they feel it should be played, rather than generate a course according to some computer's interpretation of the music. Ever play a simfile generated by Dancing Monkeys? They blow chunks.
I am also opposed to crippling demos. I dunno if you read my giant rant on the site, but I was talking about if they created a demo, I hope that they keep most of the gameplay intact. I absolutely HATE demos that either cripple the game, or limit you to a small trial period. I like the idea of using the basic game, without any of the fancy things, like online scoreboards, and maybe some of the more advanced characters (and unreleased ones), and other nice things that really add to it. I am more inclined to pay for things that make me think I'm getting bonuses above and beyond the regular gameplay, not that I'm simply paying to use the whole thing. It's the mentality.
If things are too crippled, I just go out and get a crack, because I'm either not going to pay for the functionality that it adds, or I simply can't afford it.
Yeah, I'm a bit pragmatic about my views on all this, but I'm a good example of the mentality of a number of people on the internet. I'm the guy who goes and downloads TONS of music, but I'm also the guy who buys the CDs when he can afford to, simply because its better that way.