This is one of the most extensive and helpful posts I’ve read on how to write college admissions essays. My feeling is that most English teachers know their great literature, but are not as versed on teaching writing–especially narrative style pieces. I agree that the best place to get ideas for unique topics, as well as learn how to structure these more informal essays, is by reading what others have written. You have collected a wonderful assortment of sample essays. Reading excellent writing, especially the New York Times, is also very helpful, especially feature-style articles that use creative writing techniques, such as anecdotal leads and descriptive details. I try to share similar writing advice on my blog, Essay Hell.
The people reading your essays are regular human beings, which means you should write with that in mind. A good way to check your tone is to read your essays out loud. No, not in your head, out loud. Read them to a friend, parent, sibling, whatever, and if you feel embarrassed or uncomfortable by the style, then you should change it. This doesn’t mean you should add in colloquial filler words like like, um, and uh, but it means that the essay should flow smoothly enough that you feel comfortable reading it out loud in front of someone you don’t know very well (don’t actually do that, but you should feel good enough to).