Mages can't ignore pdr rate in any way, can they?

I don't think so. In fact, the only magic attack buff I'm aware of that might stack is post-reconstruction Bless. It was completely redone in terms of variables. Since the lower weapon/magic attack made it irrelivant to use in parties (Rage/Meditation is better), it becomes a pain to Heroes and Mages who have to recast each time the Bishop casts Bless. I'm assuming it stacks, but I can't exactly prove it. All Spadow says about it is the increases in the stats, but Fiel's extraction says the variables were replaced as well.

Google's, ahem, "loose translation" of the new Bless:

In my personal experience, it does NOT stack. With ANYTHING. It didn't even Smartcast in GMST. I am still rather bitter -_-