I find I don't value mastery as much, but mostly 'cause I raid with a holy paladin and a lot of it gets wasted. I have been considering trying to haste reforge, but I'm not quite sure if I'm there yet, item-wise.
You aren't. Honestly, until you hit 515 ilvl without the meta, maybe 511 ilvl with the meta... it isn't really worth considering. Once you go deep haste you see a huge potential to accidentally oom yourself. Like, before you switch you should have feel like you have to be a little reckless with mana to oom.