You probably won't even have to have the rear triangle spread. I'd grab the rear wheel from the Trek and shove it in the Miyata. Decide if the amount of hand force you have to exert to get the wheel in will drive you nuts. If it does, spread the frame. If not, don't bother. All of the other parts should transfer just fine, except maybe the bottom bracket, if you want to swap the cranks, which you probably don't need to do.

Me, I'd put whatever parts I liked best on the frame I liked best, and then sell the other bike. But, then, in over thirty years of riding, every bike I've ever owned has been a frankenbike, including the only two I ever bought new. The OEM parts spec is always a compromise. Well, actually, the bikes I build are compromises too, but they're my compromises, not ones made by somebody else with different constraints, priorities, and preferences.

--Shannon