Pirating did not kill the dreamcast. Lack of sales did. and YES, pirating did have an effect on that, perhaps even moreso than most other systems, but it did not kill it. It came down to the fact that Sega was in a financial crisis and its baby Dreamcast was getting beat up by the competition. The piracy most certainly did not help, and I am in no way making excuses for it, but it did not kill the system. Piracy has also hurt the PSX and PS2 but since it is selling so well in both the hardware and software market, it is not hurting Sony to the degree that it could be. That is the difference in the two cases.
And as far as piracy destroying the market value of the Dreamcast, that is just absurd. In the video game market, no companies *sans the one or two still planning to release games for it* are making ANYTHING from it. Therefore, there is no company-affiliated market for it anymore. As far as collectors go (which I consider myself) no amount of copies will ever destroy the value of a real game. I still to this day buy Dreamcast games, even if I already have a copy because I ENJOY HAVING THEM. That is why a collector is interested in what he/she collects. No true "collector" would say "O, i'll just get a burned copy cuz its cheaper" They would want the real thing.
That's just my .02 of course and opinions will of course vary, but I think it's pretty clear that the market value for the Dreamcast is slim to nil for many more reasons than piracy. The sole reason the dreamcast is even still on the radar is because of enthusiasts and true fans of the system. Real "thiefs" have already moved on to their modded ps2's and xboxes so they don't have to pay for commercially available games.