

There are two separate issues here: The pace at which you can extract material from any given spot, and how much you can get out of it in total.
Let's assume a Q spot has 90000 points. Let's, furthermore, assume that the spot radiates 90000/100 tiles ~ 900 tiles out. Let's furthermore assume that clay extracted from it has 90000/100 = 90 Q, and that, for each unit you dig out, the spot loses one unit per quality of the stuff extracted. (Extracting one unit of Q90 clay reduces the clay spot to 90000-90). Let us then assume that the spot regenerates 100 points per ten minutes of rainfall, or somesuch. It could, perhaps, be regenerated by other factors as well. Composts, fertilizers, what have you. Depending on what type of spot it is. It might also be a good idea if you factored in the distance at which you extract harder, so that you can't easliy exhaust the spot by grief-mining at the perimeter of it. It might also be cool if the spot took much longer to regenerate if it had been mined harder, so that you had to "milk" it, in order to ensure a constant flow of high Q stuff. Mine it too hard and it would take ages to bounce back.
Assuming we port the villages to the square claim system, they would be able to have almost infinite claim areas. This way it could be feasible for villages to control far vaster tracts of land without having to build a gazillion authority objects. You could thus protect at least the most meaningful uptake area of the spot.
Something like that might be an interesting model.