Rascal, mulch is really great for gardening in Florida. It not only keeps weeds down, it also cools the soil (shade from the sun), helps prevent your soil being washed away from around your plants by the heavy rains in summer, and as it breaks down it slowly adds organic fibers to the sandy soil. Mulch is a huge plus for your garden, all in all.
As to the worm castings, I think the benefit of having worms in the soil besides the aeration they provide is that they actually digest the organic matter in the soil and add the benefit of their waste products to the castings. It does have some nutrients, but as I said originally, you never know how much, or how long the will take to wash away or be used up. The 40lb. bag of castings I added to our tomato bed last fall really seemed to help a lot. At the very least, it was 40lb. of organic material added to a raised bed, so not spread over a large area, probably was more help.
