I believe it does impact wis based skills as well.
It's not that useful on it's own, but does serve a role in a party that makes heavy use of will saves, since it's a mass debuff that just sits there for a whole half hour. With Invisible Spell, or just a good chokepoint, you can set it up ahead of time, bait enemies into it, and then hit said enemies with low level mind affecting stuff like Charm Person, Hideous Laughter or Deep Slumber, which would otherwise have become obsolete due to rising Will saves.
At higher levels, it's more or less the Enchantment/Illusion version of a lesser True Strike.
Of course, it helps if you got a bunch of Mind Flayers who have Mind Blast they can saturate the area with.