I rode a 1986 Miyata 210 from December 2004 until about the middle of this July. The 210 was indeed the bottom of the Miyata 'Grand Touring' line, but by the mid 80's it was an excellent bike - full chro-mo frame, with triple-butted tubing in the main tubes. The differences between it and the 610 and 1000 are mostly in the details, though the 1000 (and possibly 610) had splined tubing, in addition to being triple-butted.
Personally, I loved my 210 and thought it was a great bike. It was around 28 lbs, stock, so it was no lightweight (especially not with all of my additions!), but it was still reasonably speedy and nimble while also being a comfortable ride - lots of fun. Sadly, I rear-ended a Chrysler this summer, and it was enough to tweak the head tube area of the frame, so no more Miyata for me
. The Surly LHT I replaced it with (SACRILEGE! I know...) is a better bike for loaded touring, but more tank-like. It's really just as fast, but it doesn't feel as zippy. I would say go for it, the 210 is a really excellent machine.