Plenty I would like to have seen but didn't - and am unlikely now to have the chance (e.g. Zeppelin, Pink Floyd etc) but then again I wasn't old enough
Am much less of a gig-goer these days. About 20 years ago I went to everything I could, mostly metal gigs, but also Stones, Queen, Bowie...
I would still make the effort these days if it was something special - e.g. I'm a big Bowie fan and would probably still catch him - did so in the point a couple of years ago. Saw Smashing Pumpkins and Radiohead in relatively recent times(!) Also, Metallica last summer & there are a few more obscure bands I haven't seen and would definitely go to if they played here e.g. Killing Joke, Voivod, King Crimson (whatever incarnation they may take!)
You say literally hundreds? Any unusual examples?
(maybe we should PM this particular tangent!)