Based on the decals and the shifter location, I believe your bike is from 1984. From the middle of the Miyata range, the 310 was a very popular bike.

It looks like your bike has either a replaced or repainted fork. It could be an indicator of a frontal crash and I recommend inspecting the front ends of the top tube and down tube for signs of wrinkling. Also, the brake levers have been changed to to aero style.

In my opinion, it is not valuable enough to warrant a full on repaint/restoration. I would suggest tuning it up, cleaning it up, and riding it.

I had a 1988 312 go through my hands, and it is one of the few bikes I have flipped that I wouldn't mind getting back.

Here is the 1984 Miyata 310 catalog page.