Maybe you guys can shed some light on this but I never "got" Valentine. He was always booked as you mentioned, always on PPVs, etc. yet I never thought his work was anything special, he was always grossly out of shape and looked boring as fuck (terrible promos, etc.)
Mind you I'm only 24 and never really watched NWA/WCW until probably 1992ish, so I probably missed his peak but at least from everything WWF I've watched I never quite saw the appeal.
Valentine was a pretty good worker when he was young, particularly in the Mid Atlantic territory.
He worked that methodical 80's heel style, and in his early WWF days he was able to drag decent matches out of people like Junkyard Dog and Ivan Putski, which was no easy task. He was a guy who knew how to work that classic 80's style match where the babyface got a million hope spots, and he was great at selling the comebacks.
He was also often paired with sub par workers in heel teams, like Brutus Beefcake and Dino Bravo.
Then he got old, got lazy, and since he was never a great athlete or anything, his stuff started to look really bad. The couldn't really figure out what to do with him. They stuck him with Honkytonk Man, but his lack of charisma was comical. They turned him face, but again, he lacked charisma and his style didn't fit the role. They used him in prelims to put over heels getting big pushes until they finally let him go around 1992 or 1993. He went to WCW, but didn't last long. I remember him in weird tag teams with people like The Barbarian and Dick Slater that never connected or took off.
If you watch his Mid Atlantic stuff and early WWF stuff, you'll see a guy who really knew how to work for the era, and did a lot of great subtle things that helped carry matches against bad babyfaces. But yeah, he never really lit my world on fire, either. Pretty bland dude, but probably had a rep for being a great hand and solid guy for the midcard.
And he banged Madusa, so whatever that means.