I totally agree with your analogy that SP is pretty much the account holder's hash power, as that is pretty much what it is. As your influence on steem increases, the more effect you can have on steemit both in terms of curation and accumulating more steem power (hence increasing your influence and you get the idea).
Those who power down really should think about what they're doing. It's for their own good to keep their steem locked up as steem power, rather than cashed out and spent, etc. Of course reward yourself once in a while, maybe take profits when steem spikes, but buy in the dip again, putting the money back into the steem ecosystem.
Thanks for the well explained post as always, Kevin. Always happy to hear from you.