My reaction on seeing that Boris Gor painting was a bit different---my first thought was to think of which Boris Gor painting of his I'd like to own! I read a bunch of books of that crazy series in my teens and early 20s (and would often skip over whole sections that were too tediously into John Norman's theories and social commentary) but generally enjoyed the covers, including the Boris ones (even the chessier ones) even if some were a bit more obvious than others.
Of the Boris ones (I think he only did 8 of the reprints) Priest Kings of Gor had a cool alien. Raiders of Gor had one of the few illustrations of the protagonist clearly from the front (a bit better than Outlaw of Gore which also had a slave girl and salve captor on it). But I wouldn't buy say Captives of Gor unless I was looking for that type of good girl (bad girl?) art (which I'[m not).
By the way, owning Boris Gor is risky based on HA archives. Nomads sold for $11.3k in 2007 then only $9.5k in 2015. Outlasw sold for $10k in 2009 then only $7.5k in 2016.
Oh, and I'm 95% in Gene's camp on the preceding discussion (I would say 100% but I'm sure there's SOMETHING I didn't quite agree with ).