I've got an 1985 Miyata 1000, and it really is an excellent touring bicycle. I still ride it a few times a year, although no longer for touring. When I bought a new bike, I discovered the Miyata didn't quite fit me right. My new bike is simply more comfortable for all day riding.
So make sure the Miyata fits you before you buy it. If it's not quite right and cannot be adjusted for your body, forget it!
Or if the Miyata needs upgrades, think twice. I replaced a bunch of worn-out parts about eight years ago, and the upgrades exceeded the original cost of the bicycle!