EBSoH increases direct spell damage as long as the spells aren't doing armor-ignoring damage. Most of the direct spell damage in an S/D/M team is armor ignoring, as Jeydra pointed out a few posts back.
EBSoH also works on wanding. For a party of 8 that is about 80 (r3) - 120 (r10) damage every ~1.33 seconds (http://wiki.guildwars.com/wiki/Attack_speed). That is +60 dps for auto-attacking.