By all means demand the sum you feel you've lost (and if the downloader disgagrees then have your day in court), but going beyond that feels like an abuse.
If you think it's reasonable for them to use the legal system to enforce you to pay then you should also understand that identifying pirates and serving them with legal notices is not free. So wouldn't it also be reasonable for them to pass this cost onto the pirates?
Of course since nobody knows what the actual cost of these "parking tickets" will be it's too early to know whether they'll be reasonable with the fines or if they'll use RIAA "math."
I'm still not sure how I feel about this. I think most of us have an aversion to using the legal system in this way due to the tactics employed by the MPAA/RIAA over the past decade so pretty much by default I don't like this idea. But at the same time the company is going to be releasing the game DRM free which is something the community has been asking for for a long time, and it's not unreasonable for them to expect players to pay for their product. It will be interesting to see how this plays out.
I'll definitely be buying the game, my big decision will be whether to go with steam (the majority of my current games are there) or to use gog (to support the DRM free movement).