There certainly are more of these than ever, it seems. In fact instead of a "dearth of successful tribute shows" I'd say we have a surfeit of tribute shows in general. But that's in keeping with a larger cultural trend (akin to the endless remakes and reboots of old movies and television shows, etc.) that this guy wrote about:http://www.avclub.com/articles...and is also talked about in the new Vanity Fair here:http://www.vanityfair.com/styl...
I'm pretty sure I also read that at Redding this year they were just going to show the film of Nirvana's performance there for one of the main time slots. Now that's fucked up. I think some of it is just simple math - Guns N Roses sold a zillion records, and had huge hit songs. You just say their name and people are going to show up. There's no reason a local band would be able to compete with that, until they have a hit song or two of their own.
From a musician's point of view, I think the tribute nights are like taking a master class in someone else's work, getting to know it intimately, and hopefully coming away from that with something that will inform your own work. It's can also just be a challenge, to see if your chops are up to it. I also totally see the parallels to acting. And if there just isn't going to be a Queen or a Bowie ever again, it's a chance for performers and audience alike to enjoy that music in a live setting, at maximum volume, with like-minded folks.
After this year, I'm starting to think that we are going to only have more and more of these. There's going to be a touring incarnation of Queen, as well as franchise Queens all over the world. We'll start to see Pearl Jam and Nirvana pretty soon, if they're not already out there. It's going to be the modern version of going to the symphony or the opera, where you see classic works by long dead authors performed by the local troupe of performers.