Honestly, even if you decided to "drop" Tampa (and I can see cases both ways on this front; see below), various points about schedule flexibility and the like speak in favor of running 2-3 trains to Florida. If nothing else, there's sweeping up cities in the Carolinas with trains (i.e. you can't really cover RGH and CHS with the same train) going both north and south.
With that said, I have to wonder about the possibility of simply splitting off a "stub" service to run ORL-TPA. Of course, if I was going to do that what I would want to do is run a DMU-based service between the cities aimed at serving commuters and simply arrange to run a through sleeper (or two) and coach (or two) through from each train. In essence you'd slap the Amtrak equipment on the back of the next SunRail train to Tampa, with some sort of allowable cross-platform transfer permitted to/from the Miami-bound trains somewhere between the two cities.
With that said, I have to wonder about the possibility of simply splitting off a "stub" service to run ORL-TPA. Of course, if I was going to do that what I would want to do is run a DMU-based service between the cities aimed at serving commuters and simply arrange to run a through sleeper (or two) and coach (or two) through from each train. In essence you'd slap the Amtrak equipment on the back of the next SunRail train to Tampa, with some sort of allowable cross-platform transfer permitted to/from the Miami-bound trains somewhere between the two cities.