I looked at doing this myself on my 5th gen, and basically from what I can tell is that there is an iridium equivalent for whatever the suggested plug is but that it merely gains you some plug life. NGK CR9EH-9 is regular and I think the iridium had IX at the end of the name or some such. Just see which plugs your owners manual lists then google "iridium equivalent for ..."
i put a set in (got em cheap on amazon.com) and really like them. no additional mileage but seemingly smoother operation.