Without A/C, a slip still has the benefits of coming and going without having to take the dinghy. It's nice to be able to walk over, take a swim, do laundry (only have done this once ourselves), get a Bushwhacker at the bar..etc.. With 6 people, not everyone may want to go to shore at the same time..etc. Being on a slip means it doesn't matter - just go when you want, come back when you want.
Only downside would be the direction of the wind and whether you'd get much of a breeze without A/C.
Otherwise it's all upside. And if you aren't using electric, I don't think much (if any) more expensive than a mooring.
The restaurant you referred to is the Top of the Baths. They are still there except the did add to their deck. Hog Heaven is on the other end of the Island and has amazing views as does the whole drive from Leverick to the Baths.
First time we stayed at Leverick and visited the Baths by land, I wondered why we didn't do this long before.
.
