This has confirmed that my own houserule, to give out Magic Points (name is a deliberate call-back to 1E) to Wizards much like everyone gets Wounds, is a sound and fair rule that resolves many of the issues with 4E magic.
You have (Will Power Bonus x 2) + Toughness Bonus + Intelligence Bonus = Magic Points. You can spend as many MPs as your Will Power Bonus at any given time. Each MP spent temporarily lowers the CN by 1, for this casting only. (To a minimum of CN 0 of course). You must always spend at least 1 MP as long as you have any remaining (even when you're casting a spell that's already CN 0; including petty spells). You regain half your spent MPs by a good night's rest.
What does this do?
It specifically means evil cultists and monsters (and high-level PCs!) can make use of the cool and strange high-CN spells, with very little impact on game balance.
Why?
Because it adds back the bonuses from Overcasting into these high-CN spells that the devs forgot to.
By this I mean that some CN 6 or CN 10 spell might read as more powerful than the CN 0 staples. But once you take the fact you will often Overcast with the "small" spells but not with the "big" ones this advantage evaporates completely.
And to be fair, if an evil spellcaster is supposed to come across as powerful and dangerous, he pretty much needs this boost. Those high-CN spells might be more damaging than the low-CN ones, but the difference isn't that great. In order to threaten a whole party, they pretty much need the boost.
Without this houserule, those chaos sorcerers would have been much better off simply plinking away with Bolt or Blast, and not bothering to use their signature spells (that make them stand apart) at all. Nobody wants that.
At the same time, this change mean the chaos sorcerer or whatever doesn't have to stand around doing nothing but mumble for several rounds. That is, the entire idea of Channelling doesn't work - it prevents cool NPCs from doing their thing before the heroes kill them.
Finally, the rules for dispelling (counterspelling) are very generous to those disliking magic. Let me assure you the evil NPC need the boost just to get off his spell at all, since a skilled PC Wizard effectively lowers the spellcasting ability of any NPC sorcerer present.
(Another indication the rules are written by people that run very different WFRP adventures than most 2E adventures I've seen. Sure, if Gotrek and Felix team up with a player Wizard, and then face scores of goblins together with half a dozen chaos sorcerers, the impact of dispelling is suitably minimized. But in nearly all adventures I'm accustomed to, there is at most one (1) evil spellcaster at a time!)
So in short, by handing out Magic Points, you ensure that every spellcaster gets a couple of chances to go for the really cool spells, their high CNs notwithstanding.
PS. Impact on play:
Mostly that it sidelines Channelling. On the other hand, it doesn't work anyway. On the third hand, it still works just as well as before for any situation where you have time to spend (such as before combat).
That is, a Wizard will still want to save Magic Points by using Channelling whenever possible. Not to mention that the number of Magic Points is limited. After you have spent them all, the Wizard is back to using the rules as written.
I consider this a small price to play to ensure that NPCs actually get off their cool spells. (Since most NPCs only live for a single encounter, they can spend their MPs aggressively) After all, the reason they're there is to scare and impress the players with their wicked magics, before they're righteously cut down as the chaos-infested dirtbags they are
