I think partly the question is of goal. Assume for the moment that there primary goals are weatlh and power for themselves, their friends and supporters, and the Republican party as a bigger entity than just "friends and supporters". (I don't include "capitalism", because I doubt this administration thinks in that way.)
I don't think most of them worry about foreign policy consequences in the conventional sense. Whatever the temporary inconveniences Iraq brings, (and I'd bet that is how Iraq is thought of in the administration) I don't think they have lost their sense of invincibility. Win domestically and you can turn the rest of the world around; if the rest of the world temporarily turns against us so much better; if the whole world denouches the U.S., the Arabs take the hit and switch to the Euro, our creditors take the hit and start selling our paper - well we (to the administrations mind) are better able to take the ecoomic consequence than they are. And the whole world being against us is a great scapegoat to rally the people of the U.S. behind us. And if the rest of the world does not get back in their rightful place (behind the U.S.) well we have nukes to force them back.
Is the Bush administration really thinking like this? Not being a mind reader, I can't be sure. But anyone think there is not a one in ten shot they are thinking exactly on these lines? One in twenty? one in hundred? Anyone think there is not at least a 1% shot that something like this is their logic? If so the question of bombing and even nuclear bombing of Iran will has zero to do with any evaluation of the what is will happen outside the U.S. If this guess is right then it will be 100% determined by domestic politics - both whether there will be bombing (which I'm guessing they have already decide or are at least leaning heavily towards) and as to whether that bombing will be nuclear.
Which leads back to a conclusion that I'm sure most of us have reached for these or other reasons - that we have to make the domestic political price of bombing Iran as high as we are able. Don't think it likely that we can stop it; but we do need to try.