Yes. It certainly does. It makes Wizar'ds communion an important spell (and I'm subscribing to the errata that says WC has to have a duration as long as the spell it's affecting, Sun duration is sufficient in my mind, otherwie, you need vis for the Aegis, vis for the WC and that botch is gonna be murder).
It could concievably blow their parma down, low level spells they have operating, etc. It resists spell casting as advertised
Spells will be resisted as the rules indicate. Regardless of realm, if the Aegis penetratees the might, it's not coming through. Does that make sense?