I was never involved in that argument about hash rate follows price / price follows hash rate, so ill chip in here I think both happens but cyclically.

As price rises so does hashrate, however hash rate lags price. As the price climbs people start to see mining gear as a better investment then buying BTC direct, so less money goes into the market and more goes into mining. This causes a cyclical top. When price tops out you still have a buttload of hash rate that is on order, waiting to be deployed, or in the process of coming online. As price drops, this puts pressure on miners to sell, and as the hash rate increases  so does selling pressure, at which point price starts to lag hash rate. As mining becomes less profitable the tide changes, all the money going into mining gear shifts back to buying cheap coin. Which drives up demand, only this time there is even more dollars chasing that limited supply (based on the principal that adoption is constantly increasing). As the prise starts to rise, miners are able to recoup their capital investment in dollar terms and start to think that perhaps holding is a better option, as the price is rising. This cuts supply and drives the price higher, and thus the cycle repeats.

This cycle exists because miners are (imho wrongly) still measuring things in dollars. When miners start looking in terms of BTC only thats when this cycle will start to break down. That's where your piece of pie comes in, and thats what people should really be looking at long term. (miners or investors). If BTC becomes money, what percentage of it do you own.

When you compare that to the present situation with dollars, pounds or whatever your local currency, you see how little you need just to 'hedge' your position. It astounds me that people don't at least buy that *just in case* especially given how little that actually costs right now.

I guess thats why banks are so rich though eh

Can someone explain me why the hashrate going up is good for the price?

I mean, I know economics. I know that the supply is a function of price and cost. So if cost goes up for miners, then the supply will shrink. But why the hashrate should be consider as proxy of cost?

It's is quite possible that the cost for most of the miners is actually going down while the hashrate and difficulty are increasing. If there is a consolidation of the mining market, big mining farms are making economy of scales, so their margins increase while the hashrate increase too, so they could very well selling a greater proportion of their mined coins to enjoy their high margin.

All of that to say that I am not convince that the hashrate is a good proxy for evaluating the cost of mining BTC, therefore not necessary a good indicator for the future price of BTC.