I believe many Norcos were relabeled Nishikis. Judging by the components alone, if they are original, it's an entry level model, though probably better than a department store bike. You can find date codes on the reverse of the Shimano components, and if they are original, to get a better sense of the model year. Check against this chart.
As you state in your thread title, I would guess late 80s.
Value? Probably not much on the resale market. But if you plan to ride it, looks like a decent bike. Interesting location for rear brake bosses.
Try posting in the vintage, retro, classic forum at mtbr.com. They know something about old mountain bikes there. Those u-brakes mounted under the chainstays were on almost every mountain bike in 1987.