Definitely don't paint if you plan to resell. You'll spend a lot in the process and the bike may be worth less in the end.
Angles do look really slack. I'm going to guess '85 or '86 (Biopace chainwheels were available as early as '83.) I think by the later 80s Gary Fisher had changed the geometry significantly towards what would become the modern MTB.
As far as value I doubt it will go anywhere over $300. My guess is about $200-225 in a decent market.