You certainly need to upgrade your lens and consider how everything fits your trip.

You did not say what arrangements you made for the Galapagos but people usually spend a bit of time on the main island (Isabela) and take a boat which stops at several islands in some kind of circuit. The other option is to stay on the mainland and take day-trips to each smaller islands but that prevents you from reaching the outlying ones and so you wont be seeing the Penguins and probably not the Albatrosses.

Other than on Isabela and San Cristobal you will be accompanied and staying on marked paths at ALL times. This is where the really interesting stuff shows up and because of this arrangement, the animals have no fear of humans and will be right next to you. This has the tremendous advantage of being able to shoot wild animals in close proximity, so you will not need any big lenses except to shoot birds in flight. A Canon 24-105mm F/4L would be fantastic and with a 70-200mm F/4 you would be very well covered. This does not give you much of a wide-angle but the Galapagos does not have that much sweeping landscapes. If you really see a shot which is too wide, you can always stitch a few shots together.

Weight and power are serious consideration in the Galapagos islands. Even on the mainland you would be lucky to have power around the clock, particularly at night, so you would be charging your batteries during the daytime while you are shooting elsewhere. For this, consider taking 4 batteries and 2 chargers, so that you have 2 batteries charging while you are out shooting with the other 2.

You will almost always be carrying your gear over distances in excruciatingly hot temperatures. When I was there in April, the thermometer reached 47C (114F) and was like that for over 8 hours a day. Contrarily to Safaris, Galapagos tours are done in bright light, so bring a polarizer but you can leave the tripod.

The best way to beat the heat in the Galapagos is to go snorkling. A number of boats will stop at strategic locations so that passengers can snorkel while lunch is being prepared. Visibility in is extremely clear and aquatic animals get close. An underwater housing would be amazing to have but those are very expensive. I bought en entire Nikonos underwater film camera system for that trip and sold it later. Maybe renting is an option, otherwise simply buy an underwater compact camera like the Pentax Optio WG-2. This will probably bring out more possibilities than anything else you can add to your gear.