I believe we’re past the point of a Holy Grail Guitar. I’ve thought about this thread quite a bit, struggling to answer. That comes down to the fact of personal taste. A ‘59 LP, as cool as it might be, probably isn’t the “grail” for a country player who might find that classic Tele or Strat to be the grail. It’s easy to pick a classic design and maybe to a lesser degree the prime years, but most people are going off old recordings of songs they love while they haven’t even picked up the actual instruments used. Add to that the example of Jimmy Page’s association with a Lester, yet he recorded some of those early classic songs with a Tele. If you ask 90% of TGP, it’s probably impossible for there to be a grail in the soulless PRS company.
So what really defines the Grail? Monetary value? Tonal value? Scarcity? All of the above? Or is it just all the right buttons that are pushed for a given player at a given moment that allows and/or helps them create music that is timeless? My grail might not be yours. I think most of us realize it’s somewhere in the middle. There’s a hell of a lotta grey(or is it gray?) area out there when it comes to guitar tone and taste.