If you are home brewing to save money, you're deluding yourself. It is about passion, love of doing it yourself, and crafting something. ROI is to buy commercial stuff on sale.
As I said, I don't homebrew because it saves me money, I started because the cost of beer I was buying made me think, "Dang, if I'm paying this much, I might was well start brewing it myself.
There is no doubt it's going to take a lot of beer to officially recoup my costs for equipment, that might not ever happen. But, I tend to brew more session beers and straight up cost of ingredients now is around $20 for me, plus or minus a few bucks here and there. When a keg of Miller Lite now runs $98, I'm able to brew a lot tastier, more enjoyable beer than that for almost $30 cheaper than buying that 15 gallons in a keg from a commercial brewery.
Granted, that doesn't include the $1000 startup investment, the propane refills, tap water bill, gas to and from the LHBS and additional equipment I keep buying to replace old equipment or just get something new. There is something to be said for it being economical, compared to buying $9 six packs a couple of times a week.
Am I saving money, probably not, but I'm surely not blowing my life savings making beer either. First and foremost I think the key is to look at it as a hobby. I've built train sets before, my second love is still 1/32 slot cars. The ROI for those things is only fun and you have to ask yourself, "What is the enjoyment of this worth?" Making beer is enough of an enjoyment for me, that I never have really sat down and run the numbers, because it doesn't really matter, I'd rather make beer than buy it, that's why I do it.
I do know though, roughly what it costs me to make 15 gallons and what it costs me to buy 15.5 gallons and when you add the tax the state gets off of each ounce of beer I buy, it's definitely worth it to continue to enjoy this hobby. Hell, I think for the tax alone on one keg here now, I can at least buy the grain for a nice session Pale Ale.