It's fairly safe to say that you should equip your priest with your Battlegroup's Meta-Game in mind, not just some default template that you find on some forums. For instance, in my battlegroup, I basically never get targeted unless one of our DPS dies, and at that point we've pretty much lost anyways, so it would be pointless for me to stack a crap load of armor for those situations.
I did used to play a armor set up for when people used to think targeting priests without dispelling or purging them was a good idea, which was before Xahlior's video was release, so yeah, it's a long time ago.
Hit as previously mentioned by Pwny is a very important stat for a priest these days due to defensive spell resists being in the game now, and of course it helps offensively dispel and mana burn. It's not really hard to get either; just get the Shat'ar Helm enchant, the glove enchant, and then pick up Sash from Steamvaults, and Lamp from Black Morass, and you're sitting on 3/4 spell hit
As for buffing COH, it doesn't really matter at this point due to the fact that you'd have to give up mental agility or improved mana burn, which would be a huge loss for how priests are forced to play in 5v5
Just remember to equip yourself for your meta-game and not some guides
