I think this is a great question.

Hmmm..It really depends on the song I guess. I think...would I pay 10 bucks extra with the promise of a rare(ish) song being played but had no prior knowledge to which one? Yah, I'd say so. If I'm paying upwards of 100 bucks for a show, another 10 won't cripple me.

I've said it before, I've never walked out of a show saying "god I wish they played rarer stuff". I've said "Man they weren't feeling it tonight" but...well you get what I mean.