well, it's pretty rare that you're not expected to ***** blue buff as an AP Carry.You would do that when you don't have a golem buff and probably won't build roa?
either way, I would, but not everyone would. I've cut all mana regen out of all of my specs and just focused on more judicious use of my spells, but seals are probably the most flexible runes for mages and you can make the call based on preference.