I wouldn't say a vast majority is tourist traffic - there are several million people in South Florida and most of the people on my flights are locals or snowbirds.
I know the south runway debate is very complicated and heated, but the local officials will just have weigh the cost of losing some votes from constituents under the flight paths to the loss of business and restrictions of flights at FLL due to delays. The delays are fairly recent in development (past few years) but after a few more years, FLL could earn a bad reputation among the general public - not just the frequent fliers. Just ask anyone if they'd rather fly out of MIA or FLL and the answer will nearly always be FLL. In a few years, people may be driving to PBI to avoid FLL.
Seems like a no-brainer to me.