I feel you are looking at the wrong metric to measure the value of autocross. If you go by seat time it is terrible, and no one should ever do it. The value of autocross is in the competition and the level of driver involvement over the 4-8 runs you get over the day. The amount of steering inputs in autocross and level of driver talent (especially in DFW) is so high that you must put the car right at ten tenths constantly. This happens in new situations every week or so, and when combined with an instructor you can learn so much in the high pressure environment.
I have been autocrossing seriously for just about 2 years with some sporadic events the year before that. However, having people like Ken O, Iain, Thomas, and David Whitener just to name a few constantly helping me, pushing me to get faster, I have developed an incredible amount as a driver. From their help I am now just tenths of a second off some of the best drivers in the nation, who all drive well developed cars on a monthly basis.
I have learned to switch from a FWD hatchback that changed its own gears to a RWD sports car, and then how to make it handle properly.
By focusing purely on "seat time" you miss out on the overwhelming benefits that autocross can provide.