Homer is right about the mojo, too. To me, mojo is wear and tear. Fingerboard crud uncleaned for decades is just that - dirt. And as someone who services other people's instruments, I can tell you that it's not nice. Buying a dirty instrument shouldn't cost more money, but less. It's simply not been cared for.
A cruddy bass is likely to be exactly that, due to lack of attention. As an example, no-one in their right mind would want to actually play Jamerson's Precision. He abused it thoroughly, and despite the great music he made on it, it would not be a good bass now. If you're lucky enough to pick up well-cared-for vintage stuff, and it works for you, well and good. But a dirty old bass is just that, and, unless you're very lucky, it will only ever be that.
*Particular dislike* Dirty maple fingerboards - yuk! They're supposed to look clean! And, as they are far easier to keep clean, where's the excuse for not doing so?
Keep your tools clean, people. You'll be so glad you did.
Rant over, sorry!