Although I don't think the site will ever be near 100% accurate on pricing, I do think it is a fun option, even if it is inaccurate. However, I was thinking as to how to make the site a little more accurate as it pertains to cards. What if there was a special permission to be attained by only a select few or maybe even a larger group that would have to approve the values input. Although imperfect, it would reduce pricing that appeared grossly misstated. The group with the permissions can gut check or even look at recent ebay auctions to gauge if the price is ridiculous. Also, prices should at some point become stale, meaning prices that are old should not count toward the median.
Also, I do think the ability to get reporting on changes in value for cards in your colleciton would be an awesome feature. I don't know how to work the tech side of it, but man, that would be a great feature.
This might be a horrible idea, but I thought I would toss it out there anyway.
Even though this idea would not create pricing that anyone should be 100% reliant on, I think it would add a nice touch to the site.