Update and question - after a little more freeway driving now, I have decided the problem is not gone, but it is better. The shimmy in the steering wheel is very slight from about 60-75 mph, but still noticeble. You do not feel anything seat-of-the-pants.
I also have noted more response to crowned roads than I would like - the car drifts to the right. It does not pull on perfectly level surfaces. The recent (<20k mi) alignment was farmed out from the shop where some other work was being done, and was with the old tires. Does it sound like it needs to be redone with the new tires, and could this also affect the slight vibration I feel? Thanks.