Your Stumpjumper is a very decent bike. The Deore II group is bulletproof. It is not as nice as a Comp or Team, which have XT II components and sometimes Prestige tubes, but still a nice ride.
I remember them being around $800ish when new. I have a 1991 Stumpjumper Comp and I really like it.
I still have my original 1989 Rockhopper Comp with the Deore II group and reciept. It was basically a Stumpjumper with slightly different geometry. It was a whopping $599 new in 1989. The shop, Eddie's Bike Shop in Stow Ohio was selling all the Rockhopper Comps it had because they were over $100 cheaper than the base Stumpjumper.
Late Eighties Stumpjumpers were $700 + bikes new. You've got a real nice bike if it's in good shape. Good luck and enjoy what's one of the best factory bikes made.