Savannah is very similar to Charleston in appearance and I usually refer to it as Charleston lite! It has good history and one thing Charleston doesn't have -- a really nice Train museum. They are close enough it would be easy enough to split time between them. They have Paula Dean's Restaurant and also the Little Bird Girl Statue that was made famous in the novel "Midnight in the Garden of Good and Evil". The Girl Scouts were originated in Savannah and you can see the home of the founder there.

The "East Coast" is about 5,000 miles long Longshadow offered a sampling of possibilities, but maybe you want to narrow it down further to a region?

The historical significance of Boston and environs would certainly make Massachusetts a top contender - from the Pilgrims and the Mayflower through the Revolutionary War and commercial fishing.

For seafood, I'm partial to lobstah rolls; however, Maryland crab cakes are mighty fine also (Annapolis and Chesapeake Bay have history too).

Regarding your timing, anyplace in peak foliage may be difficult to find accommodations, though the season is nearing its final weeks in New England.