Everyone's saying aliens. To specify, we need more non-humanoid aliens. We've got plenty of aliens that look either identical or extremely similar to (attractive and usually caucasian) humans, but very few truly bizarre ones. I'd like to see more legitimately inhuman characters.
Don't let Val fool you. We have a boatload of Twi'leks, most of them either blue or red (the two allegedly rarest colors).
For vocations, I'd say boring jobs tend to be underutilized because...well, they're boring. I'm sure there's someone out there who wants to read about an intergalactically-acclaimed chef or a barkeep on a small world, but in general they're rare because people don't find writing them to be interesting enough to keep going. We crave action, whether that be political or military or technobabble or whatever. Someone who can cut a fruit into seven perfect pieces before it hits the plate is amusing, they'd have trouble finding a partner.