yes, the water shoes are better. We had brought ours because we planned on doing snorkling in other ports. The gym shoes might not offer the same grip as water shoes would. With the water shoes your foot can flex around the rocks and provide more surface area fro traction vs gym shoes.
Bring your own. You can rent them there, but if you have your own you can use them at any port.
The falls are nice, but don't believe the descriptions on the excursions. Ours said you could enjoy the beauty as you climb at your own pace... bull... you are joined hand to hand in a long konga line and are pushed and pulled up the falls. Don't get me wrong.. its still way cool, but its not quite what we expected.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007