On the point about Green Day being a "heritage band", or whatever other term is used for a band that mainly plays older songs and does an album as an excuse to tour...
I'm a fairly big Poison fan (yes, I fully expect to be laughed at for that, but screw it... I like 'em), but I'm not into their newer stuff at all. In fact, if they didn't write a single song after Flesh & Blood (the album with "Unskinny Bop" on it... so you know it's been a long time) I would be just fine.
But at the same time I find 21st Century Breakdown to be incredible. And after watching Awesome as Fuck again last night, the songs from 21CB are better live than most of their pre-American Idiot songs. And with each new album this band seems to get new fans. It's not like all of their shows are full of 30-something people, who were in high school when Dookie came out. So my worry doesn't lie in GD becoming a "heritage band", but rather the opposite... that as some fans get older they will not be as interested. As a 33 year old I honestly feel like I'm well above the median age of fans at the show.