Even though I currently mine with 3TH+ (large for a home operation, but no mining farm by any means) I am beginning to think that it was not good for BTC to go big time so quickly.
While it's an interesting thought experiment, I think we'd still be in the same situation we are today, just on a different scale. So long as your any generated mining revenue outweighs the associated costs, the network will grow, regardless of whether the price per Bitcoin is $1 or $10,000. The only difference are the players; finding out you can make $1 a day after expenses by toying around with some neat crypto-machines is more of a niche / hobby market...whereas finding out you can make $10,000 a day would draw in the really big players.
Personally, I don't care what the price of Bitcoin is so long as it's stable. I'd love to spend what I have, but the fact that it's $470 today and could be $1,000 tomorrow doesn't help me do anything except horde.
What's the mean useful life of a mining rig now, from delivery to useless scrap that eats more in power than it produces in coins? Six months? Less?
Hard to say since it depends on electricity and/or hosting costs, but even an inefficient CoinTerra rig (1.6TH/s version) is still profitable at nearly BTC0.04 per day (~$20) at this difficulty, and with $7.20 in power costs ($0.15 per kWh). It stops being profitable somewhere around a difficulty of 50B.
