Will AdSense earnings will increase after blocking some Ad Networks, which have low CPC?
Yes, This is true but only some networks which are not useful. I have also blocked some low CPC ads on my blog.
Yes but I would recommend not to block as it could decrease the fill rate. You might see an increase in the rpm but it effects your overall earnings.
In my case, it's the same whether I blocked categories or not.
In my case also overall earnings have been decreased
Yes, This happens. I have seen many of my friends. If they are blocking too many ad networks their earnings decreases a lot.