Most of the high value (in terms of price) records I have are a large collection of UK Vertigo Swirls of the more obscure prog acts, private label and small label post bop jazz from the early '70s, a few real outliers-- De De Lind Io Non So Da Dove (which came to me with tattered shrink put on when somebody imported it, with old price stickers from US record outlets, the record had never been pulled from the sleeve). I have many Island UK pink labels, some of which fetch a price these days. (I'm not a completist in the case of full catalogs).
I did a rough list when we moved for insurance purposes and kept that rider in place thereafter.
I've slowed down in buying, not only b/c of price inflation, but the rare records are much harder to find, and the ones on offer are usually not M-. (Overgrading is now common, given the surge in record prices for old pressings).
I agree with Mike that the cost in today's dollars of the media typically exceeds the cost of the gear.