I recently did a small road trip in the US and loved it! Road trips are awesome!
Houston: Texas way of life - BBQ, Sun, Beer - need I say more? Of course there is the Space Centre - Houston - we have no problem! Also need to get a football game in, Museum of Natural History, Art Car museum and may do that BBQ next to Lake Houston
Vegas Baby!!! Chopper flight to the Grand Canyon, some track time at the Speedway. I don't gamble and I love Las Vegas. It is a sensory overload. 1 day to walk up and down the strip taking all the hotels and sights. Maybe even do a city tour with Elvis and his Pink Cadillac
Grand ol' LA. Find a place to stay in West Hollywood; oh maybe even the Beverly Hilton? Studio tours are a must; a walk down Hollywood Blvd and on the way out a walk on Dume Point Beach. As you have wheels a cheeky drive to tour the stars homes.....hmmmm
SF is great for resting the car and taking in the craziness that is Union Square and the Pier. A drive to Yosemite and Lake Merce won't hurt.
Final stop; Seattle - Space Needle, Pike Place; Science Centre - maybe catch a show at the theatre and then to wash down all the culture - tour the Nirvana\Kurt Cobain jaunts.....
This would be an awesome drive!!! Lots and lots of smile-age. I reckon best to do it over 3 weeks.