Your two examples of the causes, "back taxes" and "grandma has two wills" would be solved still in the case of Blockchain. I'm no die hard fan of crypto currency. However if taxes were verifiable on chain, wills were verifiable and unique globally, then there would be no second will.

Say what you will about Blockchain being one big slow database, it is still one big slow database of huge magnitude, that enforces global uniqueness. Again I'm not entirely sold on the premise but look at how our taxes are done, social security numbers, identities. All these problems stem from a lack of a decentralized authority. If some random credit agency says bill down the street is me, we have no concrete and secure means of verifying uniqueness.

Personally, i have been saying for years that identity should be tied to asymmetric encryption. Definitely do not need Blockchain exclusively to solve these problems, but it's better than what we have now.