Does the domain get any traffic, type-in or other wise, and if so, would you make more money from a developed site or parking it.
I don't want to disagree with Oriole, the name of the domain is also important, but IMHO, if you're parked domain is getting decent traffic, that would be the main indicator to me on whether to develop it or park it, you can always try Whypark or something like that, put your own adsense codes in there and see how the domain does compared to sedo!.
good luck.