Hi Tim, and welcome to the club!
The 1977 model is my favorite 150 for several reasons, and this one sounds really nice, but it's not worth $35,000 (not to ME, anyway). $35K would easily get you into a very nice late model 152, or even an older 172!
I'd say based on what I've read here it's worth about what he paid for it .... $25,000, if it's really that nice! The GPS is a plus, but now it's USED! He shouldn't expect to get any more for avionics upgrades than he'd get by removing them and selling them separately. The rest of the "upgrades" seem to have already been in the bird. Throw in $1,500 for the GPS, and I might give $26,500 tops, if it passes your mechanics annual inspection!
