I don't think I'd bet on it working with tourists unless prices for both the trains and the requisite buses/cabs to the theme parks are incredibly low.  Remember that, even taking tolls into account, it's not going to cost you more than about 60 bucks to drive to Orlando from Miami.

A few other issues: People who aren't from Florida all seem to think theme parks are within crawling distance of Downtown Orlando.  Universal Studios is probably a half-hour drive once you take traffic into account from Downtown.  Disney will probably come closer to an hour.

There's also the issue of perceived safety.  I'm not sure if the guys designing this know it, but the Downtown Orlando station isn't actually in Downtown Orlando.  It's about half a mile south, in one of the worst neighborhoods in the country.

It would be like running a train to Liberty City in order to get tourists to South Beach.

Not to say these issues can't be dealt with, but a lot of them are more long-term issues.  And this is Orlando we're talking about -- a city that makes Atlanta look like New York as city planning goes.

Be nice to America. Or we'll bring democracy to your country.