"I rather like the idea of making pegasi/unicorns more unique (rather than a horn/wings tacked on)" I am almost certain that time constraints make having designs that can be easily replicated and reused a necessity so if not for that I bet the animators might have tried to give them a bit of flavor.

However I think they do a good job with some of the characters. Celestia, Cranky doodle Donkey and some others. I think that it's just sort a question of "how often is this character going to be used" kinda thing.



On a more related note, I had been waiting for this artwork you had mentioned a while back, it looks pretty cool.