odd, i could have sworn it said something other than shields. in any event, moving on-
i would actually go the other route, personally (if it only blocks spell damage, then life already has something better). instead of having it be a shield, have it a be a non-shield permanent that nullifies #(~3ish) spell cards or effects cast by the opponent, and remove the additive bonus from 'spawning' creatures. or, as a non shield permanent, blocks the next x targets of the creatures you control, gaining a block per creature spawned would be bearable here.