If you have never visited it, it is interesting to visit it at least once.
To clear up the the rules, here's the whole rundown.
For free, you can roam all the interior of the main building, which does include some pricey restaurants and Rodeo Drive type shops and the Casino. You also have very limited access outside.
For the cheap wristbands, $25 adults $19 kids 4-12 you have full access to roam the resort, tour the Dig which is a good number of aquariums both above and below ground that are scattered over about half the outside of the resort. YOU DO NOT get any use of the water recreation facilities with this one.
To use the entire resort, which amounts to some nice lagoon beaches, an ok dual waterslide, a lazy river, and use of chairs on the public oceanside beach, you have to get a room at either Atlantis or the neighboring Comfort Suites. One thing to keep in mind is the property is huge and the parts of the water fun are spread very far apart, you will need watershoes for the walking.
Now, as for the food.. The food at Atlantis is very expensive, how about $2.50 for a can of pop? And, the food on the ship is definitely not free, you've already paid for it with the cruise wether you're there to eat it or not. We toured the resort with the cheap wristbands in a morning with plenty of time for an excellent lunch shipboard.
Now would I go back? Yes I would, but I just love seeing the place and am something of an aquatic life nut

If we had kids, would I spend the cash to get a room at either place? No, sorry, I wouldn't, I would put the level of pool fun on the same level with any of the deluxe resorts at WDW, definitly not even close to say Blizzard Beach or Typhoon Lagoon. Especially with the idea of perfectly good pool shipboard and the fact of
Castaway Cay, a very fun place also already included.