I have been on five Disney cruises (four on the Magic and Wonder when my children were young, and most recently, on the Dream with my daughter when she was 16). It's a great product, but the Disney experience is heavily targeted to children, and you are paying a premium for the kid-focused entertainment and kids clubs/child care. If you really love Disney, you may enjoy tea with Alice or photos with the characters, but if you are not using those amenities, you may be overpaying for your cruise.
That said, I would have enjoyed the last cruise more if my daughter had been 18, as we could have visited the adults only bars and the adults only restaurants Palo and Remy, which are excellent. I decided not to book a suite on Disney as I didn't see the value for the increased price (we did have a suite on our first cruise before pricing went sky high). I don't think they have a separate dining room for concierge guests. On Disney, I'd be more inclined to book the adults only specialties and stay in a regular cabin.
One final tip: My favorite dessert in any of the main dining rooms is the Mickey bar (similar to a Dove bar). It's not on the adult menu, but you can order it anyway. Enjoy!