We absolutely love RCI last calls, but would never ever ever buy retail to have access to them. We've had several great trips using them, and had friends visit us in Florida using them. They're exclusively last minute, but you get a feel for what areas will have availability when. Imo there are plenty of shoulder season weeks, not just mud season. The quality of resorts certainly varies wildly, though.
As for all inclusives, the few times I've looked at them, you can get better deals booking direct or through a consolidator. Now I search and filter then out.
Anyway, I'd be happy to do some searches for you to show you what availability looks like. Pick a location! Just don't buy whatever they were selling you. Buy a triennial at Grandview or some other Vacation Villages property instead.