I do not think you are factoring the increased value of bitcoin. As we ramp up to the terahash scale and within a few years at most, the petahash scale for mining operations, there will have to be an intrinsic rise in the value of coin to maintain profitability for miners.
Part of the contract deals with how much we would like to acquire and how much we should hold long term.
You're putting the cart before the horse.
There's no reason whatsoever why Bitcoin mining MUST be profitable - nothing breaks if it makes a loss.Increase in difficulty does NOT cause the value of Bitcoins to rise - rather an increase in the value of Bitcoins causes difficulty to rise (by making mining more profitable and thus encouraging more expansion of mining). At present that's largely irrelevant due to the shortage of (immediately available) supply being the limiting factor on difficulty increase.
The cause for the rise in value of Bitcoin has little to do directly with mining (mining indirectly DOES have impact on it).
I broadly agree with your view that the price of Bitcoin will likely rise - and also that that has an impact on the profitability (measured in BTC) of mining. But in no way is such a rise "to maintain profitability for miners" and in fact it doesn't do that. A rise in the price of BTC REDUCES profitability for existing miners (measured in BTC) by making it more profitable for NEW miners (as they can buy same hardware for less BTC than existing ones paid) and so encouraging an increase in difficulty beyond that which would otherwise occur. Such a rise does, of course, increase profitability in USD for existing miners as well - but at the same time tends towards making their USD profits less than would have occurred had they just sat on BTC (i.e. a loss in BTC terms).
There's no rule saying "mining must make a profit" and any arguments using that as an assumption are fatally flawed.
"There's no reason whatsoever why Bitcoin mining MUST be profitable - nothing breaks if it makes a loss."
I disagree. If there is no reward for mining.. i.e. you cant pay your electric bill. What is the point? To support people who already have coins so they can do transactions? No, there must be cause and effect..it is all symbiotic. You must have miners and it must make sense to mine. The price spike we have seen over the last week is only the beginning...
"A rise in the price of BTC REDUCES profitability for existing miners (measured in BTC) by making it more profitable for NEW miners (as they can buy same hardware for less BTC than existing ones paid) and so encouraging an increase in difficulty beyond that which would otherwise occur."
I like this. But some of does not quite ring true for the very reasons you mentioned above. BTC equaling BTC value..the coins they mined earlier have increased in value while the people looking for new hardware are waiting for it to arrive and have generating nothing. The person who starts the soonest will always have the highest profit.