I bought my last bass specifically so that I could mod it. It is a very nice looking Korean made 6 string that I bought unseen and untried from a dealer in another country. I gambled on a hunch that, these days, CNC production means that even on cheap basses the basic construction makes them very playable and helps them look far more expensive than they actually are. I figured that the price points were achieved by using cheap hardware and electronics and that even if I replaced all of this with top quality aftermarket stuff (Hipshot, Delano etc) and paid out for a good setup I would have a bass that played well and sounded great for around £1000 (still only a nudge more than a mid priced bass over here)
I bought it on the basis that it had a two week return window so that if the basic quality was rubbish I could send it back.
My hunch paid off. The bass looks great, plays great (after a basic setup) and the basic woodwork and fretwork are great. Turns out the original Kent Armstrong pups sound great, the bridge is an individual bridge per string affair and that doesn't need replacing either, the tuners are nice enough 'Grover' types that will only need replacing if they wear out prematurely. The only thing that was an absolute must to replace was the cheap active electronics which were hissy, not very versatile and had a quirky control layout. I replaced these with a John East designed ACG EQ-02 filter preamp taking the opportunity to ground the bridge properly and shield the control cavity with copper foil along the way. These preamps are spectacular and I now have a great looking, great playing bass that can cop any tone I will ever need (including a near perfect emulation of my '73 Ric 4001).
I have been playing a long time and have owned and played some pretty upmarket stuff, and yet this cheap bass with very humble origins is rapidly becoming one of my all-time favourite basses.
My bass playing neighbour, a couple of my band mates and a bass player in the audience at our last gig are all amazed at how good this thing looks, plays and (most importantly) sounds. Most of them were convinced that I must have paid around £3000 for it - made me very smug that I'm in for less than £600 including the preamp.
So, in this particular instance modding works for me, and although I have no intention of selling I'm sure if I was unscrupulous enough I could pass this thing off for much more than I paid for it.
Incidentally, I've also modded my '73 Ric since I bought it in 1976, but only by putting the odd ding into it.
Rickenbacker 4001 > Zoom B3 > ART Pro Channel> Crown XLS1000 > Barefaced Big One