I'm going to assume you are making terrain pieces for 3D Gaming, in which case, my answers are going to be biased around that.
When it comes to 3d Pieces, and especially for Games that take place in a SciFi setting, yeah, terrain that looks the part is cool and all, but unless every single battle will be on worlds with purple trees and Red Water and green soil and pink grass, it's best to make terrain pieces be as utilitarian as possible.
But if you want to make a Diorama, then by all means, fill yer boat.
I have terrain pieces at home that are:
Deciduous trees
Evergreen Tree
Palm Trees
Sometimes I use the Pine trees, sometimes it's the Leafy Trees, and sometimes it's the Palms. Doesn;t detract from my games, depends on how easy to set them up is what I'm looking at.