I have a few signatures but only because I wanted that actual bass, if I like the bassist associated then that's a bonus.
The four signature basses I own are different enough from anything else that you can only buy them in that signature guise, ie not just a P bass in a different colour.
Epiphone Jack Casady
Yamaha Attitude Ltd II
Yamaha BB Peter Hook (BB1200S is close but rare)
Eastwood Hooky Pro 6 (same as Shergold Marathon 6 but they're crazy rare)
Weirdly, or not, just liking the associated bassist wouldn't make me buy the bass but not liking the bassist would certainly stop me buying the bass even if I really liked it. I just wouldn't want that association.
Even though its not a signature model the Hofner Violin bass has such an association with Macca it made me buy a Club bass, and in black as the sunburst still looks too Macca. I just didn't want everyone going, "Paul McCartney eh?" every time I played it.