I personally don't even bother thinking about what the actual value of Bitcoin per its unit is, because it doesn't even make sense. It's personal for everyone what he considers Bitcoin to be worth, which depends on the needs of the buying party as well. Short term speaking, you might not consider current levels to be that much of an interesting entry point, but what if you need to quickly to put wealth into Bitcoin because banks are making life difficult for you? You'll gladly pay that specific price, which at that point means that need overrules the aspect of whatever Bitcoin's true value may be. If you take into consideration that everyone has its own needs and motives to buy Bitcoin, the 'true' price doesn't even matter.
Exactly. The thing is, bitcoin's prices can be way over the cost of mining one and still be sustainable.
Also the cost of mining a single bitcoin varies from the country you are located, electricity cost, how much your miners cost and how much hashrate they are able to produce compared to electricity output, etc. So I don't know how you're going to accurately measure that 'true value'.
If there is enough demand for bitcoin, then prices will go up regardless of how much cost it is to mine a single bitcoin at the time. It'll be very rare to have bitcoin ever sit at its true value, so what's the point of trying to base it off how much it costs to mine? You don't ever hear people talk about gold's true value in terms of how much it costs to extract, because you know that miners need to make a profit, and they can only mine so much at a time.