The difference between a "fancy VT" and a VT are one has the word "fancy" attached to it.
Seriously... you can find VT in all shapes sizes and colors. Sellers just attach the word "fancy" or "rare" ,etc to jack up the price and make them more sale worthy.
The fact of the matter is there is show quality and pet quality... that is what should dictate what the fish is worth. Unfortunately there is no VT standard right now (at least not one recognized by the IBC) so there's technically no such thing as a "show quality" VT. IMO the only thing that makes one VT more valuable over another is if you can get one that was locally bred that you know isn't coming with some disease or another.
Then of course there is the most important value scale.. how much YOU value the fish. My old VT "Fish" was worth more to me than any other fish I've owned, both show and pet quality... and that is what is truly important. How much you value the fish for what he or she is.