I personally wonder about the difficulty of discovering someone's private key in their wallet.dat by brute force attack. I think this would require 2256 hashes to guarantee finding the private key with an average crack time of 2255 hashes.
I might have gotten you wrong but aren't we talking about asymmetric encryption? So for Bitcoin's 160-bit ECDSA addresses, you would need 2
80 (~ 1.2 septillion, i.e. 25 digits) generations. Far easier than cracking symmetric encryption, you don't have to wait for the next century to reclaim lost coins.