At $0.02 per KW, you are profiting on average $320.00 per month for each S7
You have to recoup your initial "investment" (purchase price of hardware + psu) before you see any profit. Even with 2 cent power (which is rare in and of itself) you won't see profit for over a year. That's why I mention ROI even at low power rates. New hardware purchased at retail price just doesn't make any sense right now.
Not necessarily. If you plan on selling the machine, say at half price, you more or less get back your initial investment back at that point. And PSUs.... I reuse what I can, but that's assume you're replacing/upgrading capacity, not adding.
Anyways... my plan is to mine for 6 months, and then see what a used S7 will go for. If I can replace all my miners with a single S7, that's a win, too!
I'm just a hobby guy, though. This is not my day job. Everyone's circumstances are different...