The most valuable street Cuda, in theory, has to be the 71 Hemicuda convertible owned by the Blake family in Phoenix. It is the only one built for the US that came with the billboard stripe. In addition to that it is a hemi orange car with orange interior, white billboard, front and rear spoiler package, and if I remember correctly it has the recordable tape machine. This car would be awesome if it was a 383 vert, much less a Hemi.
At some point it would not surprise me if a Cuda race car became the most valuable, but this has to be the most valuable street car by far.