We have cruised 3 times to CC. Twice we had a cabana and this last time we didn't.
That being said, to us, is the cabana worth it, yes and no.
The downside is the feeling of not wanting to leave it since you spent so much money on it. We didn't explore the island at all the first two cruises because we were tied to the cabana. The only time we left was to get food and bring it back to eat in the cabana. It was definitely nice and we don't regret doing it at all. I don't recommend it for first time cruisers on the island. The first time should be spent exploring the island, snorkeling, booking an excursion or just playing at Pelican Plunge and interacting with the characters and entertainment.
This last time we didn't have a cabana and we were able to do the Sting-rays, enjoy the small shops, played in the water, and checked out serenity bay while the kids played in the kids club on the island. We didn't get to enjoy any of that before.
If you have explored the island before, done some of the excursions, then yes, the cabana would then be worth it. You won't get the feeling of missing out or being tied down because you'll have experienced what the island has to offer.
If you are a first timer, then no, it would not be worth it.