I think my decision would depend on a number of factors:
I've never been on a
Disney cruise (or any cruise, for that matter). I have been to WDW way more times than I can count. I feel like, for the moment, I've done most everything that I want to do at WDW. The only things that I really want to do but haven't are minor, like eating at some restaurants. Add in the massive construction at DHS, the cancellation of SWW (an annual event for us), and the difficulty of getting the FP's that I want, particularly when the new things like Pandora, Frozen, and Soarin reboot open, and I can make a solid case for trying something new, even though it would cost us much more than a WDW stay. We like vacationing with Disney and are confident in a quality experience. If we could make it on one of the Star Wars themed sailings, that would sweeten the pot for DH!
On the other hand, for my family, right now, I'm uncertain about
DCL being right for DS3. He would likely not be comfortable with kids' activities that take him away from his parents. As the cost of these amenities are factored into the cost of the cruise, it would be money wasted. However, when he is older and ready for the kids' experiences, I'm sure DS and DH will really want to go to WDW instead of on a cruise because Star Wars Land will be open. So it's an issue of timing.
Sorry that I offer no real help to you, OP, but it was a fun question to ponder.