I upgraded the strings, pickups, pots, jack, wiring, bridge and nut on my SX. I don't regret it one bit.
I also shielded the pickup and control cavities with copper foil, added threaded inserts into the neck, and applied some steel wool to the back of the neck to smooth it out a bit. The result is a bass I'm pretty happy with. The only thing left to do is fix the alignment of the neck, although that's just nit-picking on my part.
P&W Bassists #795; Oregon Bassists #29