I thought I'd update this. I've been using the N900 ever since I fixed its port, and it's still running fine. The port did come unglued at some point, but after regluing it on with two-part epoxy instead of the melt-glue I'd used originally it's been behaving.

As foreseen, it's been useful several times to use thumbdrives on the fly.

I now wish more phones came with a full-sized USB port.