Just bring a sea kayak. You will be able to do 30 miles a day without breaking a sweat. Then you can knock down miles as quick as you want, live in complete comfort, and have plenty of time to hike all the classics. If you are too lazy to hike 30 minutes once or twice a day to some of the most spectacular sights in the world then I don't get how you would have the motivation to paddle your ass off all day in a creek boat anyway. Seriously though, the hiking is all easy as shit, quick, and super worth it.
Leif- I agree that the view from the boat is cool that still only gets you 1% of what the canyon has to offer. The other 99% lies just around the next bend of every little side canyon