Diesel Boy,
If it's been well maintained, it should be fine. I've got an '87 Pro V 150 Yamaha on a Skeeter that I bought new. Until my first daughter was born 6 years ago, I used to fish at least 3 out of every four weekends. Also fished a pot tournament every Wednesday from March thru November. Now that I've got two kids, I don't fish as much, but still get out quite a bit. There is no telling how many hours my motor has on it, and it still runs good as new.
Down here in Georgia, an '87 Ranger (363V/364V?)would have to be in absolutely mint condition to bing $6800... probably would though. It's hard to find a "like new" boat of that vintage, so it is a little difficult to say what it would bring.
I have fished out of nearly every brand of boat over the years. I'm sure I will rile up the OMC fans out there, but I never liked OMC V6's. They seem to be fairly reliable, but IMHO they are the coarsest/roughest running of all the major brands (Merc, OMC, Yamaha). Also, they burn literally twice the fuel of a comparable Merc or Yamaha. My buddy used to have the identical boat to mine except he had an XP 150. His boat was outfitted very similar to mine, we ran the same pitch prop (25"). My boat would run just a tick faster, and, no exaggeration, burned half the fuel that his used. I would also be wary of an OMC since they have filed chapter 11. They were bought out by Bombardier, so getting parts/service shouldn't be a problem... still would make me a little nervous.
Good luck finding a boat, don't blame you for looking at used, it's hard to believe what the new ones go for these days!