Having visited the Galapagos a couple of times my advice would be to go with the 35mm gear.
Take a smaller bag with you, and pack a 50, 28 and 200 mm or similar. The longest lens is very useful for some wildlife, and the 28 will be great for some of the landscapes.
A monopod or a light rtripod maybe useful. Waterproof case/bag while not indispensable is not required, I have sailed around the islands is very small boats and have never had any problem.
Take lots of color film and some BW if you prefer.
If you are lucky you may see some lava coming off in Fernandina Island. and black and white would be anatural choice for those lava flows.
In the islands you maybe really safe, if you can wander off and walk around the orange groves near San Cristobal you maybe surprised.
If you are going to visit Quito, be careful with pickpockets and thieves. Unfortunately safety has decreased a lot in the last years.
PM me if you want to talk
titrisol, Thanks! I received your PM. I may call you sometime today - if time permits.