Well, at least in my case, it only happens as a passenger. I can sit there, and I'm fine, but the instant I try to read something, watch a video, or something like that, I start to feel bad.

Actually, even a glance at my GPS while driving wil occasionally cause a twinge.

I don't necessarily think that will be the case. As far as I knew (and from re-skimming the wiki article), car sickness (and any kind of motion sickness) is caused by the brain seeing different things than what it's processing from the inner ear. http://en.wikipedia.org/wiki/Motion_sickness

So it's more up to the individual in question, then the driver (considering a normal, average car ride, not anything in the extremes).

Car sickness tends to happen when you're focusing on the interior of the car. That's what leads to the disconnect between your visual field and your mechanical sense of motion. I expect this is the main reason that drivers are rarely affected -- they're always looking out the window (more or less), so their visual sense of motion remains aligned with their other senses.

For me, it is a side effect of some problems with my vision. I hear it is curable with vison therapy, but that is quite expensive.

Maybe if you had some sort of AR setup that projected what you were interested in onto the environment. E.g., passengers would be able to read a book as if it was on a billboard floating on the horizon. Would that be enough to combat the effect?

In theory, yes. Motion sickness depends on the type of motion. A very bouncy or aggressive ride will result in more sickness, whereas a very smooth ride (such as a train) results in less. It's all about how much confusion there is between what you're seeing and your sense of balance.

As it happens, the same types of driving that are more fuel efficient cause less motion sickness. Still, driving anywhere with stop lights and other traffic probably necessitates enough stopping and starting that even maximally efficient driving software would cause motion sickness in many people.