Welcome aboard the RoadTrip America Forums!
Of all the variables that need to be thought about before a RoadTrip, the most basic is this: Is it about the trip or the destination? With two weeks from Boston, you could get anywhere in the contiguous 48 states and back in two weeks, but if you chose the far opposite corner of the country, southern California, you'd be pretty much committing yourselves to driving pretty much all day, every day, with little time to actually spend on experiencing all the places and things you'd be driving by. If, on the other hand, your trip is to be about the journey rather than the destination, then I think that you should limit yourself to the eastern half of the U.S. Doing meandering drive down the east coast, some time on the backbone of the Appalachians, poking around the south, up the Mississippi and back home by way of the Great Lakes would let you spend a bit more time 'on the ground' and yet still expose you to a good bit of the variety our country has to offer, and for around 2000 fewer miles than a coast-to-coast-and-back trip. But ultimately the basic framework of your trip is up to the two of you. Once you have a basic plan, people can be of \more specific assistance, but the flow you're going to go with is your call.