On the "Cantina" too, I wanted to touch on something: short cuts.
One of the common tropes in both Fantasy and Sci Fi is to paint one race with one culture, one over-arching outlook, and one religion. While in general this bugs me (Why is it Humans are the only ones who have different cultures and religions?), it lets you do something else: it lets you have different, easily recognizable, and easily relatible categories right out of the gate. As a DM, if you want different cultures to be represented by countries of humans, then you need to draw a big world map - if you don't, then you can just drop that on your race, make a blanket statement "Elves = Hippies" and you're good to go. Instead of recognizing those differences by clothing or accent, you can have it summed up by physical appearance and race.
This also lets you do other things far, far easier. For instance, racism. In our world, we are can easily divvy people up into "them" and "us". But in a Fantasy world, it's even more obvious; they aren't even the same SPECIES. So racism makes "more sense". It lets you play with those prejudices in a much "safer" manner. There might even be moral gray area - is being prejudice against Orcs the "right" thing to do, since practically all orcs are pretty vile? How far can you take that - lynching orcs on site is acceptable, or "too far"? So unless Nationality is more important than racial identity (Eberron, for instance), then races make an easy catchall for baked-in tension.
Personally I think a human-centric world, the humans would likely eradicate other races, or be more prone to it. Because they are rarer, it definitely goes back to the "Hey it's different kill it", or at least ostracized that race and stigmatized it.
But I think with a "Cantina" world, you can get away with uniqueness. Bare with me a sec; sure, the sheer variety of races might take the uniqueness away from "Just another one", but it also means that you can have a lot with many different origins, purposes, and populations, and it doesn't "raise any eyebrows". You could have 3 races which are incredibly rare, or incredibly "New", and it doesn't cause a huge upset. Race X could only occur in location Y, or they could be a magical experiment gone wrong, a single group that were endowed by the Gods/chosen/whatnot, or that PC could be the first, and last of his race without causing a big stir where ever he went. It's much harder for a weird race to "lay low" in a human-centric world, but even if a PC is unique, hiding among the other many races might be easier.
This is one thing I do with some of my campaigns. I dislike including ALL the sheer number of races, not because of variety, but because of issues of overpopulation. If you dumped all the races, all the monstrous races, all the monsters in D&D into one world, they'd have died a thousand times over due to overcrowding and no food. So what I do: whatever races the PCs choose to play with their first characters, those are the "Common" races of the world. Any other race is Unique - New to the scene, Forgotten and Re-emerging, One-of-a-kind, or otherwise special in origin.
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