Move your house to before the sandy part.

You can deflate your tires to 15 or 20 lbs. This increases the footprint of the tire and helps to prevent you from getting stuck. Build up momentum before reaching the sandy part, try to keep your momentum up and don't stop in the sand. Hope this helps.

Depending on how long the sandy part is, some old fiberboard/plywood as you suggested is a good, if temporary way to go. I've got to cross a little wash on the way to my building site, and for the last three years have kept a bunch of old junky plywood there to ease the transition into and out of the wash, and get over the bits where a conventional car might get stuck. If you can afford it, perhaps you should look into getting a vehicle with 4WD. It's hardly a conceit to have 4WD and high ground clearance if you're driving to and fro in the middle of nowhere.

Have you checked to see how deep the sand really is? Driving through there and digging it up is OK if it's not TOO deep, and you don't mind getting the shovel out of the trunk (you do have a shovel and a few chunks of plywood in the trunk, right?) and digging out the subsequent crown between the two wheels. Besides, sand is handy. I'm grabbing the sand from my driveway for the underlayer of a native stone patio outside the back door of my cabin. Doubt I'll use 1/100th of what's down there, but city people pay good money to get that sort of thing delivered and here nature gives it to you for free. Same thing with rocks. All you have to do is invest the labor.

Like another poster said, get a good head of steam going and just plow on through the stuff. Perhaps you could get a bunch of old tires and nestle them down in two tracks at that spot, and there you've got yourself a free cheesy "paved" section. Plenty of old tires lying around in the desert just waiting for somebody to take them home.

Post a pic when you get a chance. And enjoy the adventure!