A good professional fix is to plug the hole, then inlay a close-as-humanly-possible piece of veneer to match up with the surrounding top grain pattern. Followed by a tedious finish touch-up. Won't be the cheapest, but definitely do-able. In my experience, it's easier to hide a fix like this on dark wood.
Cheap and dirty fix might be as simple as a black rubber grommet, which would be seen but not readily noticed in a cluster of black knobs. But we're talking about a Series bass here. Like you said- charm and value retention.
