An extended haste lasts 4 minutes. If the armor of speed is 5 base and extendable to 10 that doesn't seem bad as a single target ability that cannot be dispelled.
It does sound expensive on the SP hitting a full raid party, but not bad. If they aren't great hasters they still have better than potions and cleric/fvs's so I'm thinking it won't hurt to let bards, wizzies, and sorcs maintain better group hasting ability.
Since it's unlikely to stack with haste just let someone else haste and add a different armor buff. I'll take it.