I think it would be nice to see a history of the Stock value to gauge item availability. The Rate tag gets skewed by this particularly when Stock==0; an item isn't selling slowly because no one wants it - it's selling too quickly for the supply to meet the demand. And if you could compare the difference between when the Stock drops versus actual sales to track when stale auctions expire, that'd be cool too.
If this is too database intensive, perhaps the records only be kept for items that members have in their Item Watch lists instead of the full AH list.
As an example, I'd been watching the Earth Staff for about a week. Checking while I'm at work during the day there were about 3-4 in stock. By the time I'd get home to buy them they'd be sold out. This happened every day, until the weekend when to Stock-surge hit and I finally got one. The Rate was only tagged as Average, though the demand was higher than what could be gauged by a simple Number_of_sales/time calculation.