It may be useful to model it as an agent, but I quite doubt that it is more useful to model it as a superintelligent agent than it is to model it as an agent of some lesser intelligence.

The governments of the world could, at great cost to themselves, but not beyond what they could withstand if necessary, I think, destroy bitcoin.

If bitcoin was a superintelligence, I think it would have dealt with that already?

Just because something can be modeled as an intelligent agent in some respects doesn't mean that it has extreme intelligence.

The agent that is bitcoin is only one part of the agent which is the market. People mine bitcoin because they want to, often because they want to profit monetarily. They profit monetarily because people want bitcoin. People want bitcoin for a variety of reasons, but mainly for either speculation, or for ease of certain types of monetary transactions.

If we say that bitcoin wants btc to be mined, what does gold want? Does gold want gold to be mined? I realize that there are of course differences, and important ones, but I'm not sure why they contribute much to bitcoin being modeled as intelligent.

I suppose that the possibility of bitcoin changing as a system in a way that people agree on might change something, but I'm not sure how much.

If bitcoin were truly optimizing for the amount of bitcoin in existence, and was able to modify itself to this end, why wouldn't it remove the block reward halving feature?

No, instead, the rate of bitcoin production mostly aligns with the originally intended schedule. The difficulty is adjusted over time in order to keep the time between blocks relatively constant.

The incentive for miners is not "If you use more computational power, the (expected value of the) amount of bitcoin produced will be greater, and you will get that extra amount.". It is "If you use more computational power, the amount of bitcoin produced will be the same, but you are likely to get a larger proportion of it.".

It doesn't act by incentivizing people to take actions which cause there to be more bitcoin (uh, on the margin I mean). As incentivizing people is the only way that it acts, it therefore doesn't act to maximize the amount of bitcoin produced.

So, it is not an agent acting to maximize the amount of bitcoin produced.