Source Blizzcon 2011
Faster weapons only affect signature spells. For the wizard, you almost always want an signature spell since its free and is affected by weapon speed. Spells like disintegrate will be affected by weapon speed in the way of how fast it ticks. With the meteor spell, you want to focus more on weapon damage rather than speed.
You said casting speed is related to weapon speed. What are you doing to promote faster weapons for spells such as meteor?