Agreed on getting "locked-in" dates. We were lucky with both the Wave Nationals and the Key Largo Steeplechase. It seemed no one had much going around that time and so we just started doing them automatically the first weekend in December for the Wave Nationals and the second weekend in December for the Key Largo Steeplechase.
It seemed to work.

Also, we have always had the Tradewinds during MLK weekend.
Most of our reasoning for scheduling in the Keys is that we have to try for "off Season" times or the room rates are really high.
Believe it or not, there is a window of slowness in the Keys right after New Years until late January where you can negotiate some better rates.
Same with my Rick White Sailing Seminars we hold every April. We have to schedule them for the last two weeks in April or we run into high room rates from high season and Spring Breakers.
Rick