: My main concern in posting this is whether gelcoat is too soft or
: too thin to wet sand aggressively.

You definitely need to be careful, as worst possible outcome would be to sand through the gelcoat to the point that the laminate shows through. Although British boats traditionally had thick gelcoat, since companies like P&H and Valley have adopted modern manufacturing methods, that's no longer true. On older boats with serious damage, I've started as fine as 320 grit and progressed up through 1500. You can see an aggressive restoration of the deck of an Anas Acuta in my "Gelcoat Repair & Restoration" album at: http://community.webshots.com/user/brian_nystrom-reg