after not reading that last eight pages, I say amp... you can make a crappy bass sound/feel decent enough to gig with some tinkering... get a nice amp with a 12 band on it, lower your action, and youve got a nice setup... ive been doing it for a couple years now... i bought a nice upright instead of a thousand dollar bass (which is being built now)...
really, as long as you have sliders on your amp, your set... you can change just about everything.. most of the time what cheap amps cant do well is take out gross mids... sure, if you looking to sound like jaco it will work fine, or are looking for a really middy jazz sound... but if your playing in your average rock group, this isnt the case...
im talking about from the ground up that is... sure, if youve got a decent amp now that can produce a good amount of sound, go for a nicer bass... I just havent ever seemed to need one that much to pay for it... basically Im building one now because i feel like it...