I'm thinking that my above post was a bit flippant, and not helpful - But I think you can make that into a nice bike, with just a little work.
IMO, buying a bike like this is an opportunity to learn, and become your own bike mechanic.

Pick up a copy of Lennard Zinn's "Zinn and the Art of Mountain Bike Maintenance".
Numerous editions of it - Pick one that covers the era of your Nishiki.
It will talk you through every tool and procedure needed to refurbish that bike.