Exactly! As I have posted before in other threads my favorite track is a dirt track, NOT CLAY! Track is usually very wet. All that is needed tire wise is one good set of 11's. While this track likes new tires they aren't necessary. I am running the same set for the 3rd year in a row now. Consistently make the podium on these "old tires."
I have seen this too with just back yard tracks. Here in southern Maryland we run a backyard circuit of about 5 tracks. For the clay tracks I prep...nothing crazy just about a days worth of work and then keep them wrapped. On my personal track though its a really sandy mix of dirt. We water it like crazy to keep it tacky, but tire preps just don't matter on this track. Its all driver and time in kart.