I haven't played an arcane mage in awhile, but based off of what I did, arcane is more of a support spec than an actual spec. Fire is for pve and burst damage, Frost is for survivability and CC techniques, and arcane is for general support. It's talents are usually to increase mana, damage, resistance, etc. I wouldn't advise being full arcane spec, or even have most of your talents in arcane. I'm sure there are other mages (who probably know more) who will say that you can do very well in arcane, but imo arcane isn't that great by itself. When I respecced to frost I had less downtime, more damage, and less dying, but that could just be because I'm better suited to play a frost mage.