Opinions please

As some of you know I am planning next years trip. I thought I knew where I wanted to go, but now i am not so sure. I had planned on going to New York and D.C. for a week each. Then I got to thinking if this was the best way to spend my vacation. This is where all your comments and opinions are needed. I still want to go to New York and D.C., but i thought about cutting the time I would spend there and going to four places instead of two. So I've already decided on New York and D.C., what would you think of possibly Boston and Pennslyvania? Or are there other places in the East I shoud go? Please help me out in deciding where to go? Ciao