I think war taxes are fine as they are. I mean, it may seem like abuse to get a big roll of cash every January 1, but the new war exhaustion factor makes me considerably more cautious. Even if I can regain the lost stability in six months, the war exhaustion can be a real killer at times.
We don't want to make the war taxes useless - they should be attractive in some situations. But the concomitant risks of +1 RR plus +1 WE make a nice balance. In a short war, they may seem like an exploit, but they can also be a pressure to wrap up any war quickly. If you take out WT three times in a six year war you are asking for trouble, especially in non-core, non-culture provinces.