Two questions: Where in FL are you, and how light do you sail?
The T4.9 works great for my wife and I (280-ish). There are a good number in Florida (5 in Pinellas County alone), and all are actively raced. If your crew weight is 315 or less, you should consider a T4.9 with a 17 sq. meter chute. They are similar in speed to the Hobie Tiger, but weigh 170 lbs less, and the sheet loads on the chute are a LOT lighter. At the first US T4.9 Nat's, 3 of the top 4 teams were male/female...something few bigger boats can claim.

That said, I'll respond to each of your criteria:
1) Handicap number - Not quite as low as the I20, but close to the Tigers, and dropping steadily.
2) Designed for spin - The boat was designed for a spinaker.
3) Has class rules that allow for the lowest minumum crew weight - Not only is there no minimum, but the actual competetive weight is lower (270-320), much closer to a H16 than ANY of the options.
4) Has a strong enough presence that there would be races in the US where it could be raced 1 design - There will be several races during the upcoming year in which that will be the case. The First Annual T4.9 U.S. Nat's had 8 boats, and there was only 2 months notice!
Please feel free to let me know if you have any more questions. If you would like to sail/race my boat at one of our club races, come on over. You and your wife are welcome to take it out any time.
Thanks,
Michael Coffman
T4.9 #32