I've been wondering this too and haven't been able to find any estimates. By "paid-in capital" I think you are trying to get at how "leveraged" the holders of bitcoin are, or how much non-cryptocurrency was used to buy the bitcoin relative to current "market cap". This is complicated by the mining costs incurred and by the fact that trade for other cryptocurrencies obscures the source of funds. But understanding the distribution of how rich bitcoin holders feel would help a lot to understand the market.

Yep. It would be an interesting exercise. IMO bitcoin valuation is more or less btc-based assets minus discounted cost of btc network. Me thinks it’s negative right now.

Do you mean the sum over all blocks of block reward times bitcoin price at time of mining?