This math has already been done (see https://en.bitcoin.it/wiki/Power_Calc). Right now it's (theoretically) profitable to generate bitcoins; that would change if the exchange rate goes down.
I saw it pointed out somewhere that bitcoins are meant to be rare, and that once the final bitcoin is generated, as there's meant to be a set ammount, there will be many orders of magnitudes less of them than dollars, euros, or the etc. So, even if the cost right now is high, having a hash of them could become worth a great deal.
That is of course speculative, but when there's going to be 1 bitcoin for every 600,000 of today's dollars...assuming the sum of bitcoins becomes worth a thousandth of that of dollars, each bitcoin will be worth 600 dollars...run a mining op for one coin a day for a year(365 coins), hold onto it for a while, average the price down to 300 dollars a coin...sell for a hundred grand...
So running a bitcoin mining opp, or even buying the coins at current market value, is a feasible long term high risk investment. I wouldn't suggest putting all your eggs in that basket, but I would suggest adding the purchase of the occasional bitcoin (or the cost of mining) to your list of high risk investments.
When bitcoins become rare why won't someone else start a new bitcoin2? I think there's an asymptotic max price that can't be crossed.
The rules are as follows:
1. Every string of bits that is a bitcoin is also a Bitcoin Prime.
2. Currently I own all extant Bitcoins Prime, but I'm willing to sell them. Right now I am willing to sell them at a 50% discount relative to Bitcoins, so you can get twice the Bitcoins Prime for your US dollars.
You'd be an idiot to buy Bitcoin when you can buy Bitcoin Prime at half the price, right?