Thanks for the feedback. The only "case studies" I found were limited to really small potatoes - like "every $ spent generated $5 of revenue" - but the totals were risible - something that didn't justify the time, even at a fraction of the minimum wage (not to mention that revenue != profit. If your profit margin was < 20%, you were losing money - and even at 20%, what's the point of changing 4 quarters for a dollar?)
One site boasted of a 4,400% net return. Sounds good, until you look at what it was. $30 ad spend to sell a dog for $1,400. Not exactly something you can repeat on a daily basis. Twice a year if you're lucky (and the dog's not). And no follow-up on how much it cost to sell the next dog (a year later, despite updates to other stats in the "study", that figure wasn't - so it's safe to guess that it was a one-shot affair, and that any money spent after just inflated the original cost).