I would be fine if it were an option, either through an artists setting to turn on/off, or on each piece - as Linda said, added to the comments field if an artists wants it to show it on a piece. For myself, I really do not want my DPW sold prices to show, so if they were to show & not optional I would reduce my gallery of "sold" items to only a few that I was fine with showing. Any sales I did outside of DPW I would remove.
I see a distinction between an auction house & an online gallery. An auction house, such as eBay, does auctions & sales. I know of many buyers who check the sold items to determine what price is a good or average one to pay. I also know many sellers who check the sold items to determine what the going rate is. Art is a bit different in that you can't compare a Nan Johnson to a Claude Monet (LOL) - but people are also judging the website or gallery they are checking. If there is too many cheap ones, it will lower the average price. And that is a concern - with so many people selling their art for very low prices on DPW, it lowers the average for all. Show those sold prices & it lowers the expectation on what the price should be.
A gallery is a display of work, available and sold. Similar to an artists website, it shows a body of work of an artist. What they currently have available & what has sold. I honestly can not recall an artist website that lists the sold prices on their paintings.
DPW is a bit of both - auction & gallery. And with Art Tracking, it's a bit of a personal database of work, sales, prices. That makes it a bit more complex for adding a substantial change to it's presentation.
As you said Alix, it is a huge subject with no solid answer. I just don't see where a buyer seeing other artists works that sold for $1 is going to help me get a better price on my work. And if I were to do an average price those $1 will lower that average price. Perhaps making it optional for an artist would be the only alternative.