Want to be a little bit empirical?
There's something really cool called The Gunning-Fog Index. Gunning-Fog index (and its relative, the Flesch-Kincaid scale) are used by journalists and authors to run a quick test on how accessible their writing is (called "readability").
For example, news magazines like Times, New Yorker score anywhere from 11 to 14, scholarly texts 16-20+, and casual novels 9 and below.
You might quickly notice that the Gunning-Fog is an imperfect system that uses syllables to measure how advanced your writing is and that the index breaks down for small quantities of text, but I'm not here to argue with you about the technicalities. It IS interesting to note some of the results it gives us, though.
Cristen's essay: 8
Laura's essay: 7
Ahmed's essay: 10
My MIT essay: 11
Yan's first entry: 13*
A college essay I've read that "tried too hard": 15
* I put Yan's writing here in comparison because I believe she writes very effectively (and I'm sure you'll agree with me) with her vocabulary. Even though her writing score is a little bit on the high side, she is still a very expressive writer. Thus, she is the perfect counterexample to trusting the Fog Index too much - I'm not warning you against hard vocabulary/sophisticated writing; I'm warning you against not understanding what you're writing about.