That's relevant to both the SP30 and the S3 equally. The advantage still goes to the SP30 regardless of what the price of BTC does.
No, because Bitmain prices the S3 in BTC. Currently the S3 is significantly cheaper.
I agree that the 0.58
BTC per unit price of the S3+ currently is cheaper, but it also works in reverse. BTC shoots up to $800 a coin and it's not. In any case, that's not relevant to hosting. Hosting advantage goes to the SP30 - it's less rack space and less power consumption.