You're right, I wouldn't opt for Atlantis -- I'd wait and go there by land for a few days (it's fabulous)!
I'd ask the shore excursions desk if hotel beaches on Paradise Island allow day trippers. If so, it's certainly close enough to catch a taxi to for part of the day. I prefer going to beaches independently and we've had lots of good recommendations from the shore excursions staff over the years. Let me know what you end up doing!
Luisa Frey Gaynor
Family Cruise Editor