You really can't see much of Lake Powell in day, the lake will overwhelm you with it's size. Where are you launching? They have a really nice hotel on the water at Wahweap. On the other hand Lake Mead is also big, but there isn't much to see, one day on Mead and you'll be bored, but there is plenty to see and do in Vegas. I would try and hit LHC on Thursday and stay until Sunday so you can get a feel for what it's like on the weekend. I would also recommend the Nautical so you can leave your boat in the water. They have some suites with kitchenettes in case you're tired of eating out after a week. There is plenty to do and see at LHC, especially on the weekend.