I think the saltwater on the wheel isn't worth talking about. The sand on the tires getting onto the chain is probably more of a concern. From what I've seen, the biggest problem is probably getting your shoes and socks wet.

If your sense of whimsy says you need that picture of you dipping your wheel then go for it. I (along with thousands of others) did it in the Missouri and Mississippi when I rode the RAGBRAI. I have the pictures to prove it. The whole RAGBRAI experience was rather whimsical, in hindsight. These days I don't think I'd go to all that trouble unless I was riding coast to coast.

Take off your shoes and socks, take your panniers, tent, etc. off your bike, carry your bike on your shoulder down to the water, take your picture, and go dry your feet. Or don't.