That grind after 500 is fierce.
What are you doing to find the higher level items?
I'm finding that the PVP modes are giving the best items on a more consistent basis.
Strikes have had a low return rate for me.
Once you hit 540, only certain challenges give you +5 or greater powerful rewards, so you'll want to do all the of the Dreaming City challenges first after reset. After you do all of the dreaming city stuff, then you do the nightfall, particularly the "get > 100k" challenge. Then you'll want to do all of the weekly stuff(crucible, strikes, Ikora, Flashpoint) these will grant you +1 powerful gear. You don't really have to do dailies any more, but if you do only do them to get gear that closes the gap on all of your stuff to make sure their all within 1-4 power of each other. Ranking up Crucible and Gambit gives powerful rewards too.
Your power spikes from the Dreaming City and raid. I just ran the raid up to Riven and I went from the 560 I posted last night to 572 as of this post.