Hey Jeff,

In the Miyata production line the 310 was pretty low end. the higher the number the higher quality frame and components.
Their models ranged from 100-1000. I personally owned a 912 and absolutely loved it. I've ridden my dad's 400something and its nice too.

I'm a big fan of steel frames. Older aluminum frames can be a little sketchy, especially around the fork.

If the bike needs ABSOLUTELY nothing it wouldn't be a bad idea to try it and see how you like the feel of road bikes. However you can also find some really nice modern road bikes for around $250-350 used that would probably be more comfortable, have more upgrade options and weigh considerably less. If you have to spend any money on this old bike you might end up paying the same amount as you would for a newer bike.

Things to consider about older bikes.

Old school brake levers usually don't feel that solid or comfortable, upgrading them will cost about $25 for some tektros.
Downtube shifters might not be what you are looking for. Upgrading this if you go for anything but stem-shifters can be very expensive.
Single Pivot Brake Calipers work...but not that great. New Dual pivots will run you at least $40 unless used. ***Recommended Upgrade
Old wheels are heavy and if they aren't true or have hub issues that can't be easily fixed, the rebuild will cost you more than the bike itself so pay attention when looking at it! Look for wobble on the rim next to the brake, on the cassette and listen for strange sounds.
Old rubber tires crack easy. Replacing these adds to the cost.

The most important thing is if you like how this bike rides.. If it works for you, totally go for it. $150 shouldn't be too low of a starting offer.

If it were me, i would either find an old steel frame of higher quality, ride that bike "as-is" for a while and upgrade to a new drivetrain and wheels when appropriate or just look for an inexpensive newer bike on craigslist. you can always resell your bike if you don't like road bikes or want something nicer.

I've bought and sold 10 bikes in the last 2 years and only lost money on the first one. The rest were sold at cost or at a small profit for my time and labor.

FWIW i bought my Miyata 912 w/ Shimano 600 (former ultegra) for $250 and a Bianchi Limited w/ Shimano 600 for $250. Very nice higher quality steel frames that i upgraded to modern components.

The most important thing is that you have a quality frame that fits right. The rest can be changed.

sorry for being long winded.

Good luck!