I totally agree on these.
I was in Gold Coast Sea World last yr (See my dolphin) and has the opportunity to visit the "behind the scene" recently launch (I think). I personnally view these captive animals/fishes as sort of like spokesman for their species so that humans can understand them better. Hopefully with the new found knowledge, their wild species will benefit from them.
As for performance, its part of fund raising and as long as they are not ill treated, I dun see why not.
As for Sentosa dolphins, I had visited them once but personally I do not know if they are doing any research works on them beside performance.
Just my 2 cents