Pete - we have the same yearning for the Musicman signature tone...I've often tried either A) giving up and just keeping what I've got or B ) looking at fairly exotic but 'same old Leo design' Jazz 5ers.
I come back to the Musicman basses....every time.
Yes, a cutom builder can get very close with similar pups/positions/EQ...but, and this is the big but, only a Musicman sounds like a Musicman. Even the Sandberg basses with the H in the right place sound different....cleaner, more modern, less growl and punch.
It's cool to have variety though, I agree, but everytime I hear a Ray, I hear the tone I wanted from when I was 11/12 years old listening to lots of different genre's yet still have that Musicman tone. Incredibly distinctive.
It's quite easy to mimic a 60s/70s Jazz tone...but I've yet to hear anything sound like a Ray. It is, in my opinion, the best bass tone. Closely followed by a P bass, and then the Jazz.