I've been to Planes of Fame at the Chino Airport a couple of times, and if you're an airplane buff its worth a stop. It is off the direct route from Palms Springs to San Diego, but its not far from I-15 which is a major north-south freeway and would take you down to San Deigo via Temecula. If you're coming from Palm Springs and you want to do this, the best route would be west on I-10 to Beaumount, and then west on the 60 towards Riverside as it splits off from the 10 at Beaumont. The 60 is a good, fast freeway although they are doing upgrade work to it, and I'm not sure when they'll be done with that (widening it,and lengthening the carpool lane coverage on it). It's my primary route between Palm Springs and LA since its usually not as busy at the 91 or 10.

Chino Airport is about 5 miles west of I-15 and about 5 miles south of 60, so its not that far off the freeway. You can spend a couple of hours though walking through the exhibits. My complaint about the musuem though is that a lot of the displays aren't well explained -- although once you realize what you're looking at its amazing. (How about one of 3 Japanese-built Me-163 Rocketplanes? just hanging on a wall, with virtually no explanation...) Also, there are a lot of vintage aircraft which are based at Chino airport. While we were there, we watched a pilot rev up and fly off a B-25, and then watched a number small planes come in and snatch up advertisting banners they were going to tow over the beachers of SoCal that day (A tow line for the banners is held up between what look like 20-30' long bamboo poles. The small plane which is towing a hook flys low above the poles and snags the banner and pulls the plane up while gunning the engine. The banner is snatched off the ground and towed behind the plane.. pretty exciting to watch, particularly if they miss the banner or mis-hook it and have to drop it and return for another pass.)

For a route from Grand Canyon to Joshua Tree to Palm Springs, there are a couple of options. Probably the most interesting and scenic is to take I-40 west to Needles. Then just outside of Needles to catch the "National Trails Highway (old Route 66) to Amboy. Then from Amboy you'll turn south, go over a small range of mountains and come into 29 Palms from the north and east. That lets you be on part of old Route 66, and you can stop at the recent volcanio cone of Amboy Crater.

Your alternative route would be to head south from the Needles area via I-95, and then head west to 29 Palms at Vidal Junction. That's an interesting route for scenery, since its out in the middle of nowhere (even more than the other route), and if you know where to look there are some abandoned airbases and military training based and mining towns not far from the route.

My preferred route from 29 Palms would be to head west to the Western Entrance of Joshua Tree National Park (about 10 miles more west), and then transverse the park to come out the south entrance near Chiraco Summit. (there's a George Patton Musuem at Chiiraco Summit, since he trained his tank crews in the dessert near here). That'll put you back on I-10 about 10-20 miles east of Indio and Palm Springs. In Joshua Tree, some of the interesting places to stop include Samuelson's Rocks (about 2 miles off the road -- its a hike to and from them), driving out to Keys View for a Panoramic view over the dessert and Banning Pass, Jumbo Rocks (for rock scrambling), the Cochella Cactus forest, and the old Mastadon mine (sealed off near Cottonwood at the south end of the park -- another day hike).