I couldn't disagree more. I saw the original lineup of Twisted Sister reunited in 2005. I thought they would be washed up, not even all that great at their peak in the '80s, and ultimately just going through the motions to fund their multiple (one assumes) divorces and/or addictions. The only reason I attended was because it was a free concert at Edmonton's city fair, and I figured, like you, that it would be comedic if nothing else. To my surprise, they put on an amazing show. They played "We're Not Gonna Take It" near the start of the set, and then challenged anyone who only came to hear that song to leave. I didn't see anyone leaving.
And I don't think anyone who has seen Iron Maiden recently would call their show over the hill, even if the band members themselves are.