So, getting back to the subject at hand, it's impossible to say what the price of bitcoin should be based on it's production costs alone, even if I granted that production costs have any effect on bitcoin's price whatsoever (It doesn't, since "production costs" are simply the redistribution through inflation of the currency at a fixed rate.).
Agreed, if you see the updated paper it pays a lot of heed to subjective valuation, the fact that people hoard, sentimental or speculative reasoning etc. The low cost producer will earn excess profits if subjective demand drive the price up. What the cost of production ends up being is a lower bound, so let's say the opposite happens and there is very little market demand for bitcoin - the price will drop as there are few bids. After time, miners will just stop mining instead of incurring daily losses. Eventually supply will meet demand at whatever low price it may be. Obviously the supply of bitcoin itself is regulated at 25 per 10 minutes or so currently, so what I mean more accurately is the supply of miners will be reduced - and the lowest cost producers would be the only which remain. Bitcoin also has the feature of difficulty adjustment - so again assume the demand and price both drop causing miners to exit. The network hashpower will drop and it will take longer than 10 min. to find blocks on average, resulting in a lower difficulty. The lower difficulty has the same effect as raising the price in terms of $ x BTC/day. You can either raise the price or raise the # of BTC expected per day to induce miners to return.
The reason somebody wouldn't produce gold with a cost of $1M per oz. is they would quickly go out of business providing there are many other gold producers who operate at a marginal profit.
As for demand spurring investment this is almost certainly true - the issue is that it can lead to 'mal-investment'. A good example is happening now with shale oil producers.