HashCash for anti-spam ???

[AliceWonderMiscreations]

What if transactions themselves had to have proof of work, random data so that a hash of a transaction had to contain X 0's at the start such that it takes a typical PC 6 seconds or so to create a transaction.

That would add to the cost of creating a transaction and the random data could be pruned by nodes once they confirm a block as valid. It may reduce the number of spam transactions.