Washington is another place on the list to visit. But, like you mentioned, it is a place to spend more than a couple of days to properly visit.
The main difference I see in the roads in the big cities up north and the roads in the big cities down south are the pedestrians. Herds of pedestrians walked out in front of the cars in both Boston and NYC no matter that the car had the right of way due to a green light. That doesn't happen in Houston, Austin, Dallas, Miami, Los Angeles, Phoenix, or any other place I've been south of the New England states. Denver has its little oddity, where pedestrians have the catty corner crossing at intersections, but the pedestrian traffic is still governed by light signals.
Still want to go to Rome and London. Friends of mine are in England right now. They are posting on FB pictures of their visit to Stonehenge, the London Tower, and the Queen's Palace. They are super tourists but they look like they are having the best of times there. Not envious at all - just happy they are fortunate to enjoy travelling. Someday I'll get to go that way too. Retirement is around the corner! (Okay. A little envious.)