I understand where you're coming from and am critical of some aspects of this show, too. But I think for the band they are looking at this as the most "relevant" thing they could possibly do - being the openers for the next big thing in terms of live entertainment, as they see it.
Also don't think the comparison with Nirvana works...totally different kind of ethos as a band from U2 in their rejection of fame. For the Clash, sure U2 was inspired by punk rock bands musically but their desire to be live music innovators on the biggest possible scale is very different, too.
As for Elvis and Vegas...Bono has fully noted that connection already in the Zane Lowe interview so they aren't shying away from that. As Edge noted once, too: "right in the middle of a contradiction - that's the place to be." They've been living that tension since the beginning.
These are all valid points. I was getting a bit carried away in my rhetorical flourishes. Your phrase that interests me most is "biggest possible scale."
You're right that that has been part of their ambition since very early on (or part of Bono's ambition--I doubt any of the other three cared that much, and I suspect Larry always looked at bigness for bigness' sake with very skeptical eyes).
It could be that exact ambition has resulted in certain moves that alienate some: this Vegas thing and the SOI iTunes debacle, for instance. Then there's the Popmart tv special...the release of Rattle and Hum as a "major motion picture" rather than as a humble rock doc...etc?