Didn't read the whole thread but here's my take:
In my world (backing up oldies acts on major shows), I see all manner of cheap guitars and basses except for Affinitys. Them I never see. But for example, our guitarist uses Squiers and Epiphones almost exclusively, and I use an American Precision most of the time now but I've been known to show up with many different cheapo basses for very large gigs, including SX, Danelectro, Jay Turser, etc. The Platters' former singer Sonny Turner's musical director uses an 80's Squier Strat, Felix Cavaliere from the Rascals' bassist uses a Mexican Jazz, and one of Herman's Hermits' guitarist shows up with a Japanese Teisco Del Ray hollowbody guitar from the 60's, and they all sound great. Some of that is because they really like their axes, some of that is because they don't want to fly with a nice guitar or bass.
BUT...
We already got the gig, know what I mean? Now if your playing is really good, you will find a gig no matter what bass you use, but there is psychology involved in landing gigs. And many folks who would hire you do listen with their eyes. I know...it's unfortunate and wrong...but it is what it is and no amount of righteous indignation will change it. So while I won't say it's necessary to upgrade, you will almost certainly have an uphill battle landing gigs unless you are really good, and/or you can do reverse psychology on them..."Yeah, I could use a more expensive bass, but I can't find one I like better than this one so I stick with it." So you can either play the game and upgrade or you can try to beat the game and stick with it.