I figured out how I'm going to get my rear tire replaced, since based on tread wear I'm going to have to get that done before putting in too many miles in the ride up the east coast. I finally ended up buying the tire through REI and having them ship it to a bike shop in Saint Augustine: I've had such excellent results with the tires I've been using that it was worth the hassle to me not to have to switch brands. In general, it looks like for a trip of this length you shouldn't need to change the rear tire any more than twice (the front tire not at all), and the chain no more than four times.
I spent most of the day in Barnes and Noble looking through travel guides for the mid-Atlantic states, the idea being to find new sights for the "must see" list. It turns out that the "Newseum" (i.e. the news museum) is open again in Washington DC, John Marshall's house is open as a historic site in Richmond, and the building where John Marshall's court met is open as a historic site in Philadelphia. For example.