Those who irresponsibly held their coins and then lost access to them did not voluntarily donate to the network like the above, rather their own actions and unfortunate circumstances led to an involuntary donation to the network, as their loss becomes beneficial to the economics of Bitcoin (again, less supply).
I agree that bruteforcing is unlikely to ever be successful and if it ever is near, a patch will be implemented prior to it being deployed against Bitcoin....I hope.
There are also "dormant" Bitcoins which are kept in a cold storage wallet for later use. Some people believe these coins are lost because of the inactivity on the Blockchain. There's really no way to tell if Bitcoins are lost or dormant. But you can rest assured that BTC won't be affected just because some people lost their coins. There are plenty of satoshis for everyone to get into the game. The more coins lost, the higher the price of a Bitcoin will be.
I'd focus on buying and accumulating BTC to prepare myself for the future. Who knows if we're closer to $1m per coin than we've ever thought? Just my opinion