It's worth to buy resillance even against 1 enemy who has CC, because this item is cheap, it it counters CC 100% sure, not like Illuminate or Cauterize which items also needs a decent play to use their bonuses well. Use not many just medium amount of CC even don't worth, because the enemy team just buy this item. But mainly its uncounterableness (is it a correct word?) is the reason why I suggest to nerf this item's bonus from 30%/lvl to 25%/lvl.
Its max lvl isn't hard to buy and it just counters all CC all the time even without take care of them. CC is a secure of kill, so counter it(,) is a big deal. Nerf Resillance could restore the authority of some champions and talents, like Ash, Pip and Seris' Agony...