Slaying Dragons - Glossy vs Matte

As a self-publisher, I have my book established in two systems, in order for the book to reach as far and wide as possible.
My first stop was Amazon/KDP - a very easy process to launch an Indy-press book.
It was recommended that I also publish my book through IngramSpark, which distributes much further throughout the world, and also provides a good royalty on my book sales.  IngramSpark allows booksellers, bookstores, and distributors to buy wholesale and resell the book in their system.  This has...