If they need a debuff, how about a range limit?
For example, with 0 points into the Wand skill, the Wands range is 5.0 meters. Each point into Wands increases the range by 2.0 meters, so at 5 Wand skill, the wands range is up to 15.0 meters.
If that were done, Wands would trade power for range, and thus providing a niche role for Staves as a longer-range weapon.
It would also provide a trade-off between single and dual-wielding wands. If you want maximum range with dual-wielding, you'd need to invest a lot of points into wands. But alternatively you could stick just a single point in and put the others into Dual-wield, thus giving you 7.0 meters range but a lot of power up close.
