Dylan,
For me at least some of the appeal of the DD or other razors is simply their style and some collectability factor. I wanted a Goldedge and Wonderedge because of their often proclaimed shavability. The collector in me thought it would be fun to get a complete set, one of each. I am also drawn to certain blade contours and covered tang razors.
Lots of reasons people go for certain things and why they pay what they do. A satinedge is not that rare a piece but if it comes together with a square point, or round point, or whatever, a collector may pay more just because another just like it may be a long ways off. Two years ago I bought many, nearly mint razors off eBay for $15-20. Today if I wanted to buy any of those again I'd have to pay 3 times that because of the market.
It's all about who is watching when any of these things appears on ebay.
Tony