One of the things that annoys me the most about Trek is its tendency to make so many of its alien races anecdotal - either one dimensionl, one episode wonders or background aliens never to be seen again. I was so annoyed that Andorians, Deltans, and Tellarites are almost entirely absent from TNG in favour of carbon-copied but less interesting aliens like the Bolians, Betazoids, Zak-dorns etc.
I go back and forth on that sort of thing. Redundant alien species seem silly to me, but too much repetition of less-major species can make the universe seem small, which is often a problem with Trek in general. At the end of the day, though, I'd rather see one species developed in two appearances than replaced with a redundant species in a second appearance.