Mid frequencies, especially low mids, find themselves in any tonal conversation, whether we're talking about live or recording applications. They really are the secret sauce to tone. I've heard so many people say boosting your low mids (anywhere from about 220 to 500) will help you be heard and more present in a mix. I used to be in that camp, with a slight bump in my low mids, and a slight cut in my high mids (with bass and treble flat).
However, in recent years I've reversed my thoughts on that, and favored a slight cut in the low mids, and a slight boost in high mids to give me a little rasp, some airy punch in the articulation, and just a hair of glass on the top end. I'm running a fender jazz (60's voices) through a Markbass lm3 and MB cabs.
Tell me: 1) Where are your mids these days? 2) What bass and amplification are you running it through, and...3) How does that lend to *your* sound?
I don't think there is a golden rule. It all depends on what sound the band wants to have, what other instruments are in the band, and what do they sound like. In an ideal situation everybody is willing to work together. I dislike certain sounds but if they do work in a band/live setting I am willing to dial them in.