Depending on the quality of the sim, I might pay a small fee to see it...but for the most part, I wouldn't pay. There are too many awesome sims out there I can see for free.
If a really cool band was playing live, I might throw a few bucks down to see them. Or if a film festival was hosting in
SL, I might pay.
Overall, I think it's a bad idea, and a fad I wouldn't want to see take-off.