Please, yes, implement an iLevel restriction.

Also, neither here nor there, but higher-level content (Expert Roulette / current Raid tier on up) should have, in addition to an average iLevel requirement, a minimum iLevel requirement on all pieces that is somewhat lower. I had the awful experience of finding a tank in Hells' Lid using a level 68 weapon, iLevel 285. There's really no excuse for this at all, and said individual should not have been permitted to queue, even if they did meet the average iLevel.