+1 It really depends on price and condition. At the right price, go for it. If you ever find the Miyata you are looking for, you should be able to get your money back out of it. I routinely swap bikes out of my "keeper" fleet. Anymore, keeper just means what I am keeping for now.

As far as finding a good deal on a Trek or Miyata, you will either have to be really lucky, or look really aggressively. There is a really good market out there for Treks and Miyatas, so you will have to move lightning fast if one pops up.