I think the only thing that exposing real sales numbers would do is further bolster the ebay fiends. I think that they kept the numbers up and popularity went down, hence all the extra Wave 5 stuff. Their target audience was kids, and 5 waves in less than 3 years is hard on the wallet, let alone a kid with an allowance. After WotC got in there, there was probably a move towards seeing if the FLGS market could support Heroscape...that's your Aquilla stuff and Wave 9 and above.
Even if we knew such numbers, I'm not sure what we could do with the info...other than shop it to another game company.
My prediction (and yes, I'll check back in five years
): Heroscape gets picked up by Fantasy Flight before 2015. The game is just way too good to let sit, and FFG knows it.