Why must one choose between simple and fancy? A lot of fancy words (meaning, not commonly used) become annoying to read; a lot of simple words (meaning, most commonly used words) become boring. I say go for a normal range that isn't simplified (unless you're writing for a young audience, that is).
After all, what would one rather read:
Simple: James got home. He found that dinner was cooked and Peter was gone. It was great to have a roommate that liked cooking, because he was really tired.
Normal: By the time James got home, Peter had gone out but had left him dinner ready. It was great to have a roommate who enjoyed cooking, because he felt exhausted.
Fancy: By the time James reached home, Peter had departed but had left him dinner ready. It was superb to have a roomfellow who relished cooking, because he felt fatigued.
The simple option is what most students of English for foreigners would use, starting from the lower levels. The normal option includes words that are considered more advanced but aren't in the least 'fancy', since you come across it in lots of places. Now, 'fatigued', 'relished', 'reached home'... I have rarely come across those ones in modern novels.
Just the other day I was giving a teenager some advice: she is about to move into more advanced levels of her English studies, but is having trouble with vocabulary and structures. The funny thing is that she can do the exercises with the advanced structures, she just can't use them in her writing and speaking because they don't flow naturally in her mind.
Her favourite method of studying is reading books in the original (meaning, not abridged), which means she has a great grasp of vocabulary and most common structures. The problem is that she has limited herself to reading YA, and while I have nothing against YA, the truth is she isn't being exposed to the more complex (not fancy!) structures she needs to develop her level further.
In conclusion: It is not about purple prose and fancy words/structures vs. simple words/structures. It is certainly not about using 'elegant' and 'sexy' words. It's about using a natural range that isn't stuck in any extreme. Elegance, sexiness and proof of excellent knowledge of a language come with how you use the words, not their rarity.
If you are not confident using English in an advanced (meaning, natural) way, then by all means prefer simple words and structures. But if you feel confident with the language, don't simplify your writing. Just make sure you are not using fancy words that sound less than natural.