You're describing a one-size-fits-all vacation club, and DVC isn't that. I'm not sure that exists. RCI isn't a way to book any kind of vacation you want (cruises, etc); it's a way to exchange among timeshares. And you don't even have access to all of RCI's resorts through DVC, just a limited selection of them.
When you buy DVC, whether it's direct or resale, you're purchasing the right to stay in DVC resorts. All those other exchange options are just perks, and they're subject to change (or being taken away completely) at any time.
Buy the number of points you need to cover your stays at DVC resorts. Remember that you can bank and borrow to accumulate points. So, let's say you'll want to do a stay at WDW that costs 300 points, every other year. You buy 150 points, bank your points in the year you don't go to WDW, and that gives you 300 points to use ever other year.
As timeshares go, DVC is very expensive. For people who really, really want to be on Disney property and in villa-style accommodations, it can be a good deal, compared to paying cash for a villa. But for the kinds of 'other' vacations you're looking for, you can find much, much better deals outside of DVC. Cruises, for instance. You can find terrific deals on
RCCL and Carnival cruises. Using your (expensive) DVC points to pay for that is like paying Lexus prices for a Corolla.