Depending on what you are towing with, you could go down the Burr Trail (I think that's the name of it). There's a nice beach down there that used to be pretty secluded (it's been many years since I've been there though). Usually we would dock at the Bullfrog marina and drive our boats/waverunners around to the beach and drive the cars to the beach on the trail. It was a very loose sandy trail and my parents have got stuck in their 2WD vehicle before.
I have seen many vehicles here as well. I have been going to Wahweap the last several years to change scenery but it is a little longer of a drive. One thing to maybe consider is Sand Hollow in St George. You have the lake where you can drive right up to it and camp. You have the Sand Dunes as well as the Jeeping access and if you want to go into town and eat you can. I may be down there over Memorial and I may drag the boat down. We like Sand Hollow, you have the beach, you have a sectioned off swimming area and you have a place for cliff jumping.
Wave Runners can get pretty scary on Powell in a storm but it can be absolutely incredible where you can go. Pull up mapquest for Bullfrog and look at the west end of Bull Frog Bay.
http://www.glencanyonnha.org/maps/GlenCanyonNRA_map.pdf
Here is a map and it says North Bullfrog Bay but you can see the roads. I would call the Park Service there and ask if your set on it.