In my mind, there are only 2 things a P-bass should have as stock "upgrades" from the factory.
1. String tree that addresses the open A issues you get from the flat headstock design flaw.
2. Adjustable saddle bridge. Threaded or American style. Both would address issues with string spacing & pick-up alignment on the cheaper models.
Love it!
I almost bought a set of threaded barrels the other week off Amazon. Specifically, the E-A-three thread/D-G-four thread types they use on the current American Standards. Sadly, they seem to have sold out, so I'll keep on lookin'.