What is the source of bitcoin value? From what I understood, the economic intrinsic value of Bitcoin as a currency is based on the "CPU-work" required to produce them. That is what makes Bitcoin rare enough to qualify as a currency. Is that it?

Now the thing is CPU-work doesn't come free of social costs. Doesn't it have some incidence on things like:
- market prices of fuels (we all end up paying our electricity higher as a consequence of bitcoin, i.e. we bare the burden)
- climate change (future generations will have to pay more to survive in a less stable climate)
- no legal-compliance checks (i.e. bitcoin activity like all business takes advantage of the security of the State but doesn't fulfill the function of checking legal compliance of transactions as the banking system does - or should I say: is legally required to do)
Welcome to Bitcoin.SE! Some interesting points that you raise.

Bitcoin is more analogues to gold than more recent traditional banking.

Yes, since power is used in bitcoin mining there are some additional distribution costs certainly. The distribution infrastructure exists anyway and in most cases is not being used to capacity ex-bitcoin, however, the more additional power that a wire carries the more losses there are. If power is in limited supply because generation capacity is being reached then there are certainly additional generation costs, otherwise, the generation cost, in most commercial scale generation projects, is in most cases nothing or close to it.

I heard somewhere recently I think that the total power usage in bitcoin mining is equivalent to the full output of three large nuclear reactors. I wondered what effect that may have on climate myself at the time but rationalised that regardless of Bitcoin, practices in generation need to globally improve. In most countries people either pay for the full cost of their power or, pay the cost of generating it themselves.

It is true that the security of the state is to the advantage of all and is why people are free to engage in things like transacting with Bitcoin. As stated, Bitcoin is more analogues to gold than it is to the banking system. So, Bitcoin currently seems to be about as regulated as transacting in cash, but without the tyranny of distance, and without the value ties of fiat currency and, without centralisation. No central bank can decide to print 21 million more Bitcoin and halve the value of everybody's holdings, much like gold.

With exchanges and Bitcoin Debit Cards, Bitcoin is linked to the local banking system much like any other offshore currency.

In Australia, Bitcoin is legally just like cash. GST and other taxes are payable.