Yeah, other than adding empty transactions to the block chain I don't think one can spam oneself. I don't pretend to understand whether or not there is a problem with "block chain" bloat.

I was told that this topic was brought up in #witness. Maybe someone will take on the task of proposing something that may prevent this in the future. Whether it is the ability to remove SP delegated by @steem or a closer look at the signup process.