i get about 50/50 on the pan vs non pan sales.
I will observe that given the choice between a boring shot of the side of the car with them driving, and just pieces of track on either side vs wheels blurring and everything else being sharp and in focus, they will take the wheels blurring shot.
Given the choice between the wheels blurring side shot, or a head on or 3/4 angle shot of them behind the wheel, where you can see the look of concentration in their eyes under the helment... they pick the shot where you can see the driver.
Snyd has some good points as well, so I won't repeat them, but good shots are good shots, regardless of the technique you used to make them. If you want to sell a panning shot, you have to put it in a context that makes sense. (makes a great poster, as long as you plan to stick it in something else like a border, with the track name, etc ) the head on shots or shots with 'not normal' things going on (flying mud/tire bits/ broken car pieces) will always be more sought after because it's a moment when something odd that the eye doesn't normally notice is there.
just depends on what people are looking for 'art' or 'documentation'
I personally enjoying previewing shots at 1:1 on a big screen for people at the track. Regardless of the composition of the image, going in that far and still being able to show sharpness and details is always 'impressive'. "Yes sir, you can make this a BIG poster and hang it in the garage, no problem. we can't print em that big at the track, but we can take your order today.' That kind of backfires when it's the guy who ones a chain of sign printing companies though LOL