I was appraising a domain and read your sig and thought to myself, how completely right you are. Parking domains is flat out retarded. You are losing any potential listings you might have had to increase the value of your domain through targeted, relevant traffic.
Speaking from 11 years experience of doing business on the Internet, I love your idea. You are taking what could be a $xx domain and giving them unique content that is being indexed into search engines and as we all know, relevant traffic increases the value of any domain.
The only other thing I would suggest for your service is to add custom 404 pages with the overall package to capture any lost traffic that might have been associated with the domain prior to this person owning it.
Anyway, just wanted to take a moment to say I love you idea and that you are helping people finally learn to stop parking their domains at these parking farms.