An excellent question.
I have owned two Casady's and numerous Starfires (I'm down to two, a 66 & 67). To start, the Casady's are gone. Both epi's had neck problems that with patients and help from one of the best neck guys I know, we did get them to play clean and true. Both required using a neck press and the guys who bought them from me are lucky I was so fussy. My sunburst had a weird twist around the 10 fret and the gold one was bowed on the G string side and not the E. I believe the basses are built with wood that's just not that dry causing them to have notoriously crabby necks.
As for the sound, I think they are amazing. Different from a Guild, but impressive just the same and in the studio they are a killer, killer choice. I see no reason to mod the pickup in the JC. Even as DS obsessed as I am.
The reason mine are gone is because of the SIZE of the neck. I’m fine with the long scale, in fact I prefer them (Jazz size), but the wide Precision nut plus, the chunky depth is just too much for me while I'm gigging. The basses kill my hands. If they were cut to the size of a Jazz Bass I would still own one and play it regularly. I've even considered getting a beater and shaving it down.
They often need TLC, and you should figure it into the cost, but if you have a good neck guy and big hands…they are an outstanding bass. Clearly Mr. Casady has both (no disrespect indented).
Petey (now in Alaska)