I think reunion shows can be fun if they're not overdone and they don't continue to tour without putting out something new.
I saw the Pistols too and they were great, despite the irony in the Pistols doing such a tour.
I saw the Who on their reunion tour in 1989, and wasn't expecting much since Pete was playing acoustic guitar and couldn't hear, and the band hasd extra musicians. i was afraid it would be a Vegas lounge act. But it totally rocked. They played for about four hours (including a break) and played 40 songs (we counted). Now, i also saw them last year after Entwistle died and is was still really good (and Pete was playing electric guitar this time) but it seemed odd that they had nothing new to play.
I would definitley go see Led Zeppelin if they reformed, esp. with someone like Dave Grohl drumming