The Sociable Guru
Yoda has been dead for a long time when The Force Awakens opens, and we need someone to pick up the slack.
But it can't be the same someone or everyone will notice that it's just Yoda in a different outfit. Maybe it should be someone a little more sociable—someone who runs an intergalactic watering hole instead of being stuck in a planet-wide malarial soup, for instance—and has an eye on really living instead of keeping a social calendar that Tibetan monks might see as too quiet.
No, Maz isn't Yoda, nor is she a Jedi. She has her own plans, and she does her own thing, which apparently involves running one of those great Star Wars bars where every client looks weird and every set of eyes—even on heads that have, like, 12—has a story.
Maz believes in those eyes and those stories, which is why she has that elaborate set of goggles to augment her teeny little peepers. When she looks at you, she can see right into your soul, as she does when Finn sits down at her table:
MAZ: If you live long enough, you see the same eyes in different people. I'm looking at the eyes of a man who wants to run.
That insight lets her do a fair bit of Yoda impersonation, offering helpful tips and guidance to the right souls who come across her path. For while she may run a decidedly seedy watering hole (did you see those bug things?), she's far from a disinterested party.
Early on, she makes it very clear which side she's fighting for:
REY: What fight?
MAZ: The only fight: against the dark side.
So, not only is she on the good guys' side, but she's a lot more approachable than any Jedi, meaning that edgy folks like Rey and Finn can get a teacher who can open the door for them on their level, not from some sanctified Jedi pedestal from on high.
That's probably the real purpose of her little drink-slinging business: sifting through the galaxy's travelers to find the ones who really need her street-level insight into the Force.