Soho,
Interesting question. I can offer only a personal perspective. I think the world would be a more interesting place with the likes of Jimi Hendrix and Janis Joplin
still in it. Personally I think the influence (excuse the pun) of drugs on so much fine art (of all kinds) has been overplayed. The point about Coleridge is well made, but I feel the artists who have produced enduring works while under the spell of drugs had 'the gift' and would've done so anyway, without the narcotics. Your mention of "A day in the life" rings true, but if we go into other fields, I'd say Dr Seuss came up with some visions that match the strangeness and originality of the 'psychedelic 60s' and from what I understand he was as square as they come. As for the jazz guys, Charlie Parker was an old man (and a corpse) at the age of 35 and Thelonius Monk spent his last years as a psychological vegetable.
The artistic muse has never been fully formalised or explained, and probably will never be. We carry and find all sorts of keys that open our worlds of creativity. The crux of my thoughts on the issue of 'drugs and the artist' is that the drugs perhaps only free some of us from inhibitions that may otherwise retard out ability to be honest in confronting our psychological and emotive angels (as per W. Blake) and demons that inspire our artistic journeys. It's the freeing of oneself, the
honesty that I feel allows the artist to fly. For some, drugs may do that - but at a cost. A cost that was for some, too great to pay.