I am not sure how we should procede in Iran. But if you are suggesting that a potentially greater danger from N. Korea should inhibit us in Iran, I do not agree.
We don't do anything about NK because we no longer can do anything. We let the situation go too long.
I don't consider our tight spot with NK as any reason why we should let another crazy regime get us into a Mexican standoff.
Unfortunately, in Iran (and in Iraq previously) we would be seeing welcome greetings from the Iranians who are eager for democracy and enthusiastic that the Mullahs are gone.
In NK, you'll see no such thing. It would almost be like the would-be invasion of Japan at the end of WWII (they were expecting maximum casualties as every Japanese citizen, even the women and children, would fight to the death). NK would be similar.