Strands of Astral Power. Worth it?

[Sombre]

It wouldn't demolish any invading army. It would make bringing mages in a lot harder, but then given the restrictions of the spell - high cost, dominion only, astral pearls, high research, hard to cast, negated by enough mr (even with lots of penetration items), can be stopped by whomping the caster, dispelled - well I think it deserves to be powerful.