I enjoy encountering unfamiliar words, new phrases, and interesting description. You should not dumb down your words. Use them as long as they are correct and natural.
Isn't it possible though, that as writers we can write so that our readers understand, but yet not dumb down our writing? I am not sure big words are required everywhere as it could really knock down the higher paced parts of a story, but in the narrative parts where description is key, it would be possible to use a less common word. If skillfully written, the reader would surmise its meaning, and thus learn some new words along the way. using redundant words is not really grammatically correct in a sentence, but would convey the meaning with the need of a dictionary.
"His scattered thoughts coalesced into a single, bright vision." The meaning should be obvious from context, even if you don't know what "coalesce" means.
And that is kind of my point, it is easy enough to do. I think sometimes writers fall into the myth that writers should "write what they love" because that is NOT the main objective. That is fine if they want to do journals and blogs, but the main objective of writing is for the enjoyment for readers. As writers, we should be aspiring to adapt, change and improve our writing for that end goal.
Oh I do! I have a IRS, Schedule F Instructional manual that is pretty thick. After reading that for 10 minutes I fall asleep! I actually use it for that very reason!! I figure if I retain anything from it, then what they hay...there is nothing better than knowing what I qualify for in terms of expenditures on conservation easement's involving leased land for qualifying environmental credits. Yep, I will be better off for it. But if I fall asleep without retention, at least I got a great nights sleep.
If I have to choose between delivering complexity or simplicity, I prefer simplicity. But like others have written, we can sometimes embed a difficult word in a sentence that makes the meaning of that word understood. This can help expand the reader's knowledge, and perhaps satisfy them for a moment, in that they figured out a word on their own, perhaps making them appreciate your story more.
In this case, I wouldn't change it because it's part of the style of these particular stories. If I used simpler language, it would become something else.
This is exactly what I was coming in to post. If you word things right, the meaning of complex words becomes clear through context. This is a good way to improve the vocabulary of readers, especially in the age range you're looking at (this directed @ OP).
I actually preferred advanced vocabulary in novels more when I was an adolescent than now as an adult, since my neuroplasticity and leisure time have both declined.