Lots of derivative artists are genuinely talented. We call them fan artists and slag them until they get paid for it by the copyright owner, at which time we call them scriptwriters or whatever. They're officially extending the franchise, which is exactly the same thing they did before they got paid. Think of the guys who write the Star Trek franchise. You know they are Comic-Con going fanboys.
I think the real question going on here is whether transformative works are art or not. And are tribute bands transformative or purely imitative/derivative? I don't know if tribute artists think of themselves in the context of fan art or not but to me they seem pretty clearly related. They both come from the same place, wanting to extend the work beyond its original context.
I agree with a lot of this is general, but not really specifically when it comes to tribute bands.
For example, I definitely agree, and said as much, that some of the musicians in tribute bands are genuinely talented. In fact, in terms of sheer ability to play, I'm sure some of them are more talented than the guys they are imitating.
But I'm not sure that most pure "tribute" bands are transformative in terms of developing the music. Sure, a band who does primarily originals with the occasional cover thrown in can "transform" a song, that happens all the time, hell U2 does it. But playing a cover is much different than being a pure tribute band whose ultimate goal is essentially imitation.
Your points about fans writing their own scripts, etc. (fan fic I guess) is well taken, and for genuinely talented writers doing that can help hone their skills. But if it never leads to anything more, I really don't see the point. If you get really good at writing Harry Potter fan fic, to me that's more craft than art. And if you're in a U2 tribute band to pay the bills, and have some genuine talent, and are using that to further your own creative ambitions, I guess I don't have much problem with that. But if you're dressing up like the band and basically just imitating them...sure, it's fun, you'll make great friends, maybe get laid and perhaps even meet the band...and have a blast while doing it. Who can argue with that? And I don't have any problem with that either, I'm not saying tribute bands should vanish. Who cares, right? It's just for fun. Just don't tell me it's art. And I'm sorry, yeah, I do think these guys getting up there dressing and acting like the band look a bit silly. I guess I'd equate that more with someone dressing up as Klingon at a Trek convention (and I say this as a pretty big Trek fan). Cool looking and fun? Absolutely. But he didn't create the idea of Klingons, or design the costume, or the language.
But as I said, sure, I'll go to bar if some of those guys are playing and get a kick out of it, fair enough. It's pretty much just harmless fun. Just like dressing up like a Klingon.