I have no doubt, and am absolutely certain that . . . . .
Bass Guitar + (Amp+Cab(s) + effects if any) = Your Instrument.
The greatest bass in the world to you unplugged makes no sound. The amp of your dreams makes no sound without a bass plugged into it.
From experience, I will say if I were to spend more money on one than the other, a superior amp will make any bass better. A 10-grand Alembic plugged into a $100 amp, well, just DON'T think you're going to sound like Stanley or Jimmy Johnson. If you are a TB regular, you'll rarely see threads where guys think they're lacking a lot tone-wise when they have an SVT, a nice Mesa rig, or any good, substantial amp rig you can think of. Conversely, rarely does someone complaining about their bass sounding thin or just not right to their ears not have some combo, some underpowered or under-cab'd rig.
See where this is going? A good bass thru a big-enough amp for your needs may result in a tone that you think needs a little work, but a good bass that's running a not big enough amp pushed to its limits, having its' neck wrung almost never yields that tone that everybody wants.
I'm a card carrying member of the 'big amp turned up to 3'. I want it well within its' comfort zone, minimal distortion and lots of headroom. This is really necessary for 5 and 6 string guys, as those low C's and D's will tell you RIGHT NOW if you've 'got enough amp'. Once that's solved, then my choice of basses is way easier, as I'm hearing the instrument without the artifacts of the amp busting a gut just to make the gig.
My own two cents is that I love the little Bronco amp in my practice room, but that's the only place I'd use it. For anything else, 700-800 watts would be my minimum. 'He's crazy, that's a lot of horsepower' . . . . . not turned up to 3 or 4.