From personal experience, I'd go with whoever said, to paraphrase, spend the fortnight in California, you can always go to New York for the weekend. At the risk of getting a deluge from Americans in other parts: California is the one part of the US I always want to spend more time in, I'd spend a few days in SF and leave plenty of time to get around.
I've spent more time, for family reasons, in Florida and Tennessee and I've not been to Boston. My view of WashingtonDC is largely tainted by being chased by a drug crazed guy with a large stick!
Of course, if you want a complete list of railway attractions and museums.......