Hello.
We will always use 10x the SP you are delegating but the actual value of the upvote will vary with the price of Steem.

But then the price of Steem affects all of us, the value of our own upvotes also drops and @smartvote will always be 10x our own upvotes.

Daily payout of Steem to your wallet, that 13% annual rate will be constant. If you delegate 500 SP, @smartvote will pay you 0.178 Steem daily, but those 0.178 Steem will be worth less USD.