I generally put in something to deal with large numbers of enchantments, the choice of which is determined by the mage's training. For example: Dark = Arcane Corruption, Earth/War = Harshforge Monolith, or Arcane = Purge or Destroy Magic (depending on expected situation), or a Mage Wand with Dispel or Seeking Dispel, or a Dispel Wand.
Just as some of my books mostly ignore Battle Forges, and other books have one or two Surging Waves in them... I may or may not concern myself with removing the enchantments at all. I recently took out a heavily enchanted Warlock with a timely Dispel (for a damage barrier), and then a swarm of creatures (mostly level 1-2 zombies), so you don't always need to Purge someone.
If the Warlock had creature support, the swarm wouldn't have been enough... and a Purge probably would have been needed. To me, it just depends on how much damage you expect to do compared with your opponent. In the Warlock's case, he just didn't have the actions to support the buffs... and thus I could generally ignore the bonuses that he got from the enchantments.
Long story short, it depends on a lot of things... not just the book that you are running, but what type of mage you are facing, and how the strategies of the two mesh.
