Colo Native wrote:
do I take I70 instead of I80?
We have found I-70 preferable to I-80 across the middle of the country. Generally a lot less truck traffic and the road seems in better shape (probably because of less truck traffic).
There's more to do in Springfield than just Lincoln's Grave. Lincoln Home NHS is definitely worth your time, as is the Lincoln Library.
If you're going to Acadia from Niagara Falls, head east through the Adirondacks and the White Mountains (maybe take the Kancamagus Highway or US 302 through Crawford Notch).
We're not big fans of big cities, esp. when towing. To visit Boston, we stayed at Shawme-Crowell State Forest not far from the Cape Cod Canal. (Scusset Beach State Reservation was closed at the time). Took the train into Boston. Also could visit the Cape. Took a day trip on the ferry to Martha's Vineyard. Rented some cruiser bicycles to tour the beaches.
Newport RI has some amazing "cottages" (OK, mansions) right along the coast. The Cliff Walk allows you to walk along the amazing shoreline and look up at these amazing homes.
Mystic Seaport, CT is an interesting place to stop and get a primer on seafaring in the 18th and 19th centuries. Great for mountain dwellers like us. Lots of historic vessels.
Of all the big east coast cities to visit, Washington D.C. is #1 on our list. If you have the time and haven't been there, go! Plan on several days and just pick a few museums and monuments to visit. You can't see it all even with lots of days to do it.
Other places to consider:
Williamsburg, VA
Steamtown NHS near Scranton, PA
Monicello (what an amazing diversity of interests Jefferson had)
Gettyburg, PA
Since you "only" have a month, I'd make a beeline across the central part of the country out and back to concentrate on the sites in the east (although Springfield, IL is definitely a must do). The last time we went out, we rode Amtrak and took our tent and sleeping bags. Two days of train travel each direction then rented a car for a month. Still rushed (did spend five full days in D.C.).