I'm honestly not sure where all the bemoaning about it being too salty to use as a mulch comes from, doesn't seem to be from people who have actually tried it in their gardens as the accounts of From the Sea and Saltcayman match that of my own which is it works great used straight. A particularly effective combo I found for bananas (I have super sandy low organic matter soil too) is too heavily mulch with horse manure and then layer a thick mulch of seaweed on top of that, the bananas went gangbusters and sent roots upwards against gravity into the mulch.
I've used it for various other fruit trees too (tamarinds etc) with no ill effects, besides it having a whole host of trace minerals it also contains beneficial plant growth hormones (some seaweed can grow 3 feet in a day). If you are still somehow concerned about salt, just give it a quick hose over before laying it down. You're sandy soil is a pro in that too much of anything can easily be washed out of the upper profile of it if you water enough. The nice soils Ireland built up to grow their potatoes was from soil, manure and seaweed over generations.
A nifty trick is also that you can make your own liquid seaweed fertilizer (which can be terribly expensive in stores). Fill a bucket 1/2 to 3/4 with seaweed, add water to full, cover and store downwind from the house (can smell a bit while breaking down). After a couple weeks to months the seaweed will have dissolved completely, and you can dilute 1:10 or 1:20 with water and fertilize or spray foliarly!
Hope I've convinced you