No wonder it's tought to sell. There are very limited number of people who even remember Wasteland, let alone played it back when it was released. And based on reactions of Fallout3, how many of original Wasteland fans would even be remotely happy with end result ? Probably not many, even if sequel would be good.
I'm not sure if reanimating these old brands is good idea anyway. It's very rare that some core mechanics or world aspects would be worth to salvage vs. creating something complitely new. Personally I got lucky with Fallout3 because world aspects are the most important thing for me and I don't care much or combat system, rules or perspective as long as they work fine. But at the same time it's easy to see why many fans of the original games are very angry about new direction of Fallout3.
The biggest reason to use an existing franchise is the boost in marketing, for nothing.
The largest cost is the potential loss due to diehard fans not liking it ... which is negligible.