Simple version:
you always have the option of simply buying Bitcoins so for a miner to be more profitable it has to return MORE bitcoins than it purchase price.
Correct. It was not the most optimal decision for the best ROI. I'm chalking up the difference in returns to the value of the fun of having the unit, tinkering with it and it being a conversational piece. There's definitely a luxury non-investment component to my decision.
It's sort of like people who raise their own coop of chickens for eggs. They'll never be able to produce eggs as cheaply as efficient factory-farms or even big cage-free organic farms, but they do it anyway because it's kind of fun to make your own.