A balance dis-spell card would only make the Balance Wizard more strong. EVERY other school of the spiral relies on one balance spell, or two, or three. Be it blades, traps, weakness, and reshuffle to name a few. My balance wizard would use five of these dis-spells in the deck if it were available.
Best case scenario for other school wizards would be making the famed Judgement fizzle, but that really does not hurt the Balance wizard, pips stay and they will draw another soon. Your best bet is to reduce their damage and survive the hit and let them be pip-less.
As for the Balance shield, well, that would put the Balance wizard at the bottom of the "food chain". All there spells are moderate in damage. Judgement needs to be at least 10 pips and be bladed/trapped for it to be worth losing all pips the wizard has.
The tower shield really is a pain in the neck for Balance wizards, more than some would believe, to the point where many Warlord balance people will spend 2 pips (including power pips, and one training point) on the Ice Dis-spell.