Etymology also makes for great made up words like sanguage. A well-written etymology will lend credibility to the most stupid theories; and a good pseudoetymology is a joy to the heart.
Another thing etymologies are good for is explaining ununderstandable grammar rules, like irregular past tenses and participles in English, or bizarre pluralization rules in French.

I will now digress: my mother, being a university professor of Latin and Greek has a natural obsession for etymologies, and the rest of the family happily shares it.
A constant companion at dinner was a big, slightly greasy, dictionary with word histories, later replaced with a vastly more complete five-volumes etymological dictionary.
The moment I had some money from teaching, I immediately went out and bought a copy of the compact edition of the OED: and therein lies madness.