We're less than 30 days away from embarking on what sounds like a very similar Galapagos trip. CyberDyneSystems was a great help in getting us prepared for the trip.
It does sound like my idea of carrying "light camera gear" is the same as CyberDyne's. I plan to carry a 7DMKII & 1DsMKIII with a 16-35mm, 24-70mm, 100-400mm MKII and 400mm f4DO + 1.4x TC. My girlfriend will have the 70-300mm L and 24-105mm on her Rebel. As for cruising through the airport I'm carrying the bulk of the gear in a F-Stop Tilopa with Large Pro ICU. My thoughts are that I can pull the ICU out if anyone gives us crap on the planes....although we're flying Delta first class the whole time (purposely upgraded to reduce gear damage risks). We plan to carry everything on. Fortunately, the galapagos doesn't require a lot of packing!
I'll pack some light clothing in a duffle that attaches to the F-Stop while my girlfriend is going to have a partially empty camera bag (just in case we have to move stuff around) and a roller suitcase with our shoes and snorkel gear. My only concern is the flight from Quito to the islands because the weight restrictions are different. But I think we've done all we can to prepare for that.
As others have told you, this is one of those trips of a lifetime. Having been on a few like these before, I can assure you your only regret will be not spending the money to make this trip an amazing success. You'll totally forget the money later, but you'll never forget the experience.