Well, offcourse it's completely up to you... If you can get your hands on nearly-free gear, ad you believe the price will skyrocket whilst the diff will stay low... Sure, you can go for it... However, i think those odds are (really) small.

Personally, i would not start a mining operation if i could not recuperate my investment in 6-9 months at the current price and a diff of 30T. But then again, i'm not a big risk-taker. In reality, that would mean i should be able to buy latest gen gear from China at a fraction of the price AND have a power price that way lower than 10 cents/kwh... Ideally, in the 3-6 cents/kwh range.

Let's put it this way: if you were my close, personal, IRL friend and you came to me for advise, i'd tell you not to do it because the odds of getting burned are to big... Especially if you're going to get a loan to start this business... Banks want to get their money back, old ASIC's are worth close to nothing... So having a 50k-100k loan might make them confiscate your wage (if you have one), make them sell some of your belongings, or even your house.