All good arguments above. But one merit of the Florida HSR line is that it probably can be built soonest with minimal NIMBY/legal brouhaha, and function as a showcase line. This is very important, as few Americans outside of readers of this forum can distinguish between light rail, conventional (amtrak), or high speed rail (even the media, which should know better, frequently does this). Only 20 percent or so of Americans have a passport, with a lower percentage actually traveling to a country with real high speed rail (i.e. not Mexico or Canada). Couple this with the fact that only 2% of the American population has ever even ridden a passenger train, and you have major ignorance of the benefits of HSR. Having a true HSR up and running in a reasonable amount of time can be a game changer in terms of public perceptions and, most importantly, willingness to pay through taxes for other HSR lines. Tellingly, JR Central apparently sees the Florida HSR as very attractive, focusing its marketing push there, while pretty much leaving Alstom, Siemens, et al to fight over California's problematic HSR project.
Good things about Florida:
1) This isn't just another upgrade for the NEC. The NEC has their trains and "high speed" isn't that much higher than what they have. They will get the upgrades they need out of their own cut of funds direct to Amtrak. The stimulus is for new projects.
2) The movers from the NEC who are accustomed to corridor trains (even if only by seeing them) will appreciate the new line without ever riding it. It will be a taste of "home" for them ... as long as it isn't a drain on their retirement.
3) People in Florida vote. Sometimes they punch the wrong chad but it is an important state in national elections. The impact of HSR dollars in a Florida, Ohio, Illinois and California (who can't afford to do it themselves) is higher than in the NEC. In the NEC HSR will be seen as just a faster Acella. In Florida it will be the start of something new.
I'm probably the opposite of a NIMBY. If the government wants to spend money on HSR they better spend it in my neighborhood.