This vibrating at low speeds is very intermittent. I didn't experience it at ALL today. It comes and goes...
I know my struts need to be replaced. I'm not sure how bad the front ones are, but actually the past couple days I can hear them squeaking while driving. It'* subtle, but I'm sure it'* the struts. The rear struts are damn near shot IMO, I hear snapping noises when I hit the right kind of bumps.
The tires, well, I've been pretty sure they have been unbalanced since I got them (I swapped rims/tires with another member). I noticed since then, that I would get a bumpy ride at highway speeds, and I was sure it was the wheels/tires.
But like you said, balancing problems really don't show up until driving faster. Which is why I was concerned while at 30-40mph it was bad, but 65 it was fine. I've definitely gotten what I've figured to be tire noise for as long as I can remember. They are not great tires at all.