I've only changed out pickups a few times: Twice from whatever was in it going to a full EMG's + EMG network changeout (and oh my yes, QUITE the difference), and then I changed the pickups out on my Squier James Johnston strictly as a part of 'hot rodding a Squier fever'.
In the EMG cases, I could have left well enough alone, but I really wanted EMG's. The Squier was entirely un-necessary, but I got a great deal on some 'takeout' brand-new Fender Yosemites from a guy that, you guessed it, bought a brand-new Jazz and just HAD to update his pickups to something new.
I've never owned a bass that it was an out and out necessity to change them, so I did it only on the occasions above. For me there are SO many aftermarket pickups out there for Fender Bass-Shaped Objects, that honestly I would not know where to begin, aside from changing from passive to EMG's. TOO many choices for old JW !
Plus honestly, I always think a new amp was the quickest way to a different tone.
Other guys thinks it's a must-do and good for them if it works for 'em.