I've seen this sentiment a few times in this thread, and I don't agree.

One of the best reasons for deciding to use a nice handbuilt frame for a conversion is that it is a nice handbuilt frame. If you honestly can't tell the difference in ride and handling between your average cromo bikeboom frame and a nice handbuilt, I can see why you wouldn't bother converting one, but that doesn't seem to be the case. I have a conversion that I'm very fond of, built around a 3rensho. It was a great bike when it was geared, and it's great as a fixed gear. Nothing about the ride or handling has changed, they still kick all kinds of ass, the only difference is in the drivetrain.

A garage sale univega, while lugged and steel, doesn't feel anywhere near the same to me. That's why I convert nice bikes : because I like nice bikes.