On the one I'm just finishing up I didn't increase the size of the elevators but I did split the elevators and using one servo for each half. I did increase the length of the rudder by about 1/2" to give it a little more authority. A friend of mine suggested building up the rudder and elevators instead of using the ones supplied in the kit, so he made up new ones for me using 1/4" x 3/8" stock and then sheeting them on both sides with 1/16" balsa.
I also sheeted the turtle deck with 1/64" plywood - it looks much better and is a lot stronger.
I did clip the wing by one rib, and my friend suggested adding flaps. Most guys here haven't added flaps because the plane is a floater, but my friend added flaps to his and his definitely seems to land smoother and slower than some others without them I've seen. The worst that can happen is you don't use them if you don't like them. We just basically split the aileron 60%-40% with the 40% being flap. The inboard portion of a strip aileron just causes drag anyway and isn't very effective.
Mine should be ready to fly probably next weekend, and if not, for sure the following week. I'll let you know how it goes!