I don't equate telekinesis with magic, though it's probably more accurate if I went old school and did numbered spells, like Fire 1 through Fire 4. (Where Rarity has access to the basic magic, Fire 1, while Twilight's got all four.) The fact that there's a need to distinguish gifted unicorns from the not-so-gifted (mundane?) very clearly indicates that not all unicorns are created equal. Is it because of their destined special talent (the cutie mark crusaders make it very obvious that they won't get anywhere until they realize what their special talents are) that each individual unicorn can only go so far with their magic? I don't want to make that assumption just yet, but the relation between cutie marks and unicorn magic just isn't making enough sense to me.
The argument concerning Twilight being a librarian is faulty. You forget that the books in the library contain many magic-related things, and we see Twilight learning new spells all the time, from said books or not. I'm pretty sure that being a librarian wasn't her main, I'm-going-to-do-this-for-life pursuit, and I doubt the thought ever crossed her mind (what with being Celestia's number-one pupil). As for Rainbow Dash: pegasi fly, which invariably involves speed, and speed does seem to be a part of their work and culture, so it's only natural that some will have some kind of talent for it. If you really wanted to argue a strange cutie mark in relation to what kind of pony they are, I would have gone with Fluttershy. However, that's neither here nor there, since those are different magics from a unicorn's, and so the capabilities and expectations are different.
If raising the moon was truly satisfying for Luna, she wouldn't've cared if no one else appreciated it. And if she were a wise pony, she would have realized that night couldn't be appreciated in the same way as day, and had -- in fact -- been showing their appreciation all along.