As those things go, I found that the game itself is not enough: if you have the packaging and all original paperwork inside, such as the manual, even sales inserts, you can get a nice return on it even if used.
It's like comic books: it's all about condition too.
However, you will find lifelong fans willing to dole out for their favorite game even if the packaging is in tatters.
In terms of copies, I believed there may have been at least 150,000 made.
Not sure why I have that in head, but I believe that is the standard run for most games during that era.
Then again I could be mixing that up with records or comic books! :p
The retro game market is a strange beast sometimes. I just find it strange that complete copies of Kolibri sell for half of what this game does, when Kolibri is for a much more obscure, far less successful platform. That, and Kolibri is likely of more interest to Ecco fans given its nature theme. Three Dirty Dwarves isn't high up on my 'to get' list at the moment, but it does look interesting with its great use of the Saturn's hardware.