I've powered down. I'm getting roughly 1 percent of my SP in steem once a week. I'm still making more SP per week than I'm getting paid out of it so I will still have more SP than when I first hit the power down once the two years is done. I don't know if I'd say it's "worth" it, but having that steem that I can cash out every week is making my bills much easier to deal with. As far as I can tell the exchange rate has no effect on your power down, it only affects how much you get for it if you cash out.