yes I think it is not an easy decision, I would probably try some adsense ads for a month on the content and just see what the revenue is like from that.

I guess you could also try putting up a parking page for a few hours - you'd probably get a good idea in that timeframe of what the current traffic is worth on a park page. Would guess the type of people who regularly buy old site/link type names might be able to give you a bit of an idea on how quickly that extra traffic from development might fall if you were to go with a park page.