It would just cause players to more carefully consider what cards they play. For example, my version of Interference, it applies to any card that the player plays... So, Pillars, Towers, Shards all the way to Rare Weapons and Creatures... If you managed to get a Nova, Nova, Interference in your first turn... You could completely cripple your opponent by forcing him to lose some of his towers. It will also add a level of protection against Improved Miracle.
As for Thalas' version, I presume it only targets 'Spell' Cards? So, Firebolt, Drain Life, Rain of Fire, Quintessence and Miracle... etc??
If that is the case, then it is really overpowered. In that you force your opponent to lose a card, considering that Deflagrate and Steal wouldn't work on this Permanent. You could pretty much shut down your opponent with one card. I also don't think it should be Gravity, which seems to be getting more and more overpowered by the minute.