I played The Lawnmower Man years ago because it was part of the software package on a Gateway 2000 my family had bought. Funny that the one quote says "...nearest thing anyone's seen to an interactive movie" because that's exactly what the game was, an interactive movie. Never played the second game though.
As to value, the version I played was for DOS. I didn't know they made a Mac version. The Wikipedia article says the second game is rare and I have to figure a Mac version of an already rare game is even more rare. eBay showed the PC version of the first game going for ~$5 and the second game for ~$10 so I guess at best maybe $20?