re: Death Valley/Mojave National Preserve
not a bad plan, the Mojave Preserve would be a day all to itself to see the whole thing. Death Valley can be two days, just depends on how much time you want to spend seeing stuff, hiking, etc. There is plenty to see by a regular car but a high-clearance vehicle will let you see more on the back roads if you are interested.
a few other things to see/other stuff:
1. Amboy Crater:
http://en.wikipedia.org/wiki/Amboy_Crater
it's a bit south of the Mojave Preserve. maybe something to end your day on. you can hike into it.
2. Rhyolite:
http://en.wikipedia.org/wiki/Rhyolite,_Nevada
this is on the way to the central part of Death Valley. It's a paved drive into it. Definitely worth seeing imho.
3. Pahrump is a pretty good base for operations if you are going to head out to Death Valley for the day; obv. Furnace Creek Resort is also as you would wake up at Death Valley. IMHO starting at the south end of the park and working your way north is the best way to do Death Valley which you could do coming from Pahrump or Tecopa Hot Springs. The last thing you would see going south to north is Scotty's Castle which is pretty cool. Do the castle tour also.
4. make sure you pay the self-pay fee to go into Death Valley. I honestly didn't see it the first time I went there and got read the Riot Act by a ranger at a checkpoint in the park.
5. u probably know this, but just to make sure. Parts of these areas are a lot more remote than people realize before they head out there. Make sure your vehicle is good working condition (spare tire, hoses & belts in good shape, coolant full, etc.) and take plenty of water.