I've stayed at Casa Ybel, Sanibel Cottages, and Hurricane House. (owner, not as an exchange). All are really nice resorts. All were heavily damaged w/ Hurricane Charley August 2004, and were closed for quite some time. Sanibel Cottages reopened in April, Casa Ybel partly in May, partly in July, and Hurricane House in the same time frame. They are now good as new.
However, they are all small resorts (CY - 72 units, SC - 28 units, and HH - 15 units), so exchanges will probably difficult, especially in the peak season of March. Also, when these resorts were built, the standard was for a rather simple 2nd bedroom with 2 single beds. Not like the studio suites they build today. Just something to keep in mind.
As noted, South Seas Plantation is still closed. Captiva got hit worse than Sanibel, although it wasn't split in two. (In May, I drove up to South Seas entrance on the north tip of the island. North Captiva (another island north of Captiva island) may very well have been split though. It was all but split in a previous hurricane with only a narrow stip of sand left connecting the north part of the island to the south part. North Captiva is only accessible by boat/airplane).
Also, as noted, a LOT of trees were lost.
They are building new bridges on the causeway (there are 3 bridges), so construction will take a couple of years. Traffic can be really bad in season, but is not bad at all when I usually go in May and October. One of the bridges is a drawspan, so an opening can really cause backups. I believe that span is being replaced with a high bridge though.
Anyway, my two favorite vacation destinations are WDW and Sanibel!