If your goal is to stay at WDW, it is definitely not worth it to buy access to RCI, because DVC is in the midst of a move back to Interval.
More generally: the conventional wisdom/advice around timeshares is “buy where you want to stay.” That could mean a resort (like the oceanfront Kauai resort we love) or a resort system (like DVC, Hilton, Wyndham, etc.) Third party exchange via RCI, II, and others is always a hit-or-miss thing, because the “rules of the game” change constantly. In particular, it’s almost always a bad idea to buy a timeshare with the expectation of exchanging it regularly for a very specific purpose.
I’ve violated this advice a few times—two of my five owned weeks are at a resort I’ve only stayed at once, and I use them for exchange most of the time. But, I’ve tended to be more opportunistic, looking for interesting things and taking them when they come up. There have been some grand exchanges that I would never have paid market rate for that we’ve lucked into. Perhaps my favorite was a 3BR penthouse at Hilton’s Lagoon Tower in Waikiki. Two-story windows in a corner unit with a commanding view of Oahu, and a wraparound deck that included an ocean view off to the side.
For me timeshare exchange is a hobby. If I included the time I’ve spent on it at anything close to what that time “costs” me, there’s no way I am saving money. But, it is a fun game to play, and it’s probably better than e.g. sports betting all things considered.