For a very long time, I have been saving a batch of Urban Warfare Archangels to use as Seraphim. I did a little conversion on some of them, such as this one. Just a little arm swap.
I have had to do a bit less of the snazzy stuff that I wanted to do, but time is just not there!
I used a chunk of the Secret Weapon Broken Column set, as well as a bunch of powders. They were not just used to create weathering or exhaust... I used them to do a little painting as well.
If your work it right, you can smooth out blends, or get some interesting color variations without having to go through lots of paint mixing!