A couple of things . . .
I had a RIB, it was stolen off the beach where I live and not wanting to spend a lot of money now, I bought a used air-floor soft bottom dink. Never again. There is no comparison between a soft bottom and a RIB, the RIB is a Ferrari against the Amish cart soft-bottom.
Scratch the aluminium bottom on a rock or coral and it corrodes, drag it up the beach enough times to expose the keel, it corrodes. Successfully painting the damaged ali "out there" is a nightmare. GRP is totally forgiving of damage and in the unlikely event that it does get holed, it is easy to repair.
I'll second the 2 stroke. Lighter, smaller and in my experience uses less fuel. Easier to maintain, often quieter, less costly, how many more reasons are there?
My ideal dink is a 12ft Hypalon RIB with a 3.3hp 2-stroke OB with integral fuel tank. Mercury would be my choice - the only thing I can never understand is why they put the tiller arm on the left side and the gear shift lever on the right??
. This combination is what my dnk will be when we go off.