Makes sense. I like it, although it may be a bit too cheap to negate the activation of N spell cards, N being the number of creatures you control. Extreme case, but still.
Also, I'd like to see Light getting more permanent protection, as that's an area we can agree it has staked a claim in (immaterial shield/weapon, no immaterial creatures). If we give it both permanent and creature protection, there may be balancing problems...