From your description, a set of lightweight wheels might be your ticket. If you buy the rims and have them built up, it may cost you more than a complete set of wheels. You should investigate buying a second set and learning how to swap back and forth. (It's not THAT hard!)

A good Mavic rim is gonna run $60-$80 each, and then labor to build them up. You can get a decent wheelset for around the same money. Check out www.pricepoint.com or www.Jensonusa.com and there are many others. Pick up any mt. bike mag and scan through the ads for wheel deals.

Then, you can use your old wheels when you're planning on going with your sons off road where you might bash your wheels.

Another advantage, is you can buy a spare cassette and have slicks mounted on one set of wheels. Flip the quick release and plop on the old wheels with knobbies! 3 minutes top!

Just a thought!

L8R