I'm sure this is not going to be revelatory for most of you expert cooks. Also, I'm sure someone's figured this out already, but:
...if you want to refresh stale tortilla chips to its formerly crunchy, brittle state; use the microwave!
Lay out a few chips on a paper towel, microwave on high for 30 seconds (watch out for scorching).**
During this time, marvel at how the moisture (which makes chips stale) is evaporated as if by magic by your oven.
When it's done, you'll get warm chips ready for dipping in a cool bowl of salsa.
BTW, I don't recommend you try this on a Dorito.
** NOTE: You need the kind of microwave that has a rotating turntable, or else you will be very sorry in a my-science-project-burned-the-school-down kind of way.