You "worry" about a "habit" of invading other countries. I'm sorry, that is just ridiculous, it is not even a thought. War is not "habit forming". We aren't going to invade Canada because we "need our fix". We either see real interests furthered by war with a country, or we do not.
Then you worry about "dire unintended consequences". Anything you do or don't do can have "dire unintended consequences", starting with "doing nothing while nutjobs get nukes". Care to explain what any such consequences are, and why they might be likely, or why they might be worse than doing nothing? It is nothing more than an allegation, "something might go wrong". Duh. Something might go wrong no matter what you do or don't do. It is not an argument for or against any policy.
Then you no more than repeat yourself, saying "these mistakes can be really costly". Prove it. You can't. All you've got is an allegation about a hypothetical. "Maybe" five years from now Iraq will be worse than Saddam. And maybe the moon will turn into green cheese. Could Islamic radicals take over Iraq? Possibly, though they will find it hard to do with US troops all over the place. Could they take over the Iraq a year ago, by assassinating Saddam and having a rebellion? Sure. They didn't, but they might have. It was "possible". Is it supposed to be more possible now, with us there, than it was then, with him there? We are a hundred times stronger and infinitely more just, offering a much better life than he did. Are we still "deposable"? Sure, under president Dean or what have you. Was Saddam deposable? Definitely.
Alleging remote possible unintended consequences is not an argument. Anybody can do it, for or against any policy. It simply amounts to saying "boo". The question is whether risks increase, are made more or less likely, are risks of worse or of lesser things. You haven't even attempted to explain why e.g. pressuring Iran involves greater risk than letting them turn on their reactor this year.
You are saying you don't trust your government to decide who to invade and who not to invade. Uh huh. Who do you trust, the baby Jesus? Who else is going to make such decisions, here and now, in the real world? It is what the government is for. Such decisions have to be faced and made. That they are weighty does not mean they can be avoided. That one might get them wrong does not mean that it is safer not to make them. You don't get to not make them. If you decide not to pressure Iran, then you decide that Iran chooses whether it has nukes, not us.
You say show restraint - fine. If there is an error make it on the side of peace - not so fine. Peace is not decided by one side. It takes only one to choose war. Our enemies have chosen war, said so, acted so. We can decide where we draw the line at support for, or aid can comfort to, those enemies, yes. But we can't "err on the side of peace" if our enemies just don't want any peace. You don't get peace because you want it. You only get it if the other guy wants it. Which is mostly a matter of scaring the beejesus out of the nasty ones.
Are all of anybody's plans going to turn out how they want them to? No. Not theirs, not yours, not active, not inactive. The world isn't like that. It is an argument against a straw man. You worry that it might "blow up in our faces". So it might, so might your course of action of doing nothing, or as little as possible, or stopping now and announcing it to everyone (dumb just as strategy, even if in the end you do). There isn't any course of action that might not blow up in our faces. The question is, which is more likely to? And you've given no argument at all why e.g. leaving Iran alone is less likely to blow up in our faces than pressuring them is.
Of course we are doing reconstruction stuff in Afghanistan and Iraq. There is no distraction from any of that involved, no reduction in ability to do it. Nobody expects to do anything further until after the election regardless, and after that everyone hopes that pressure alone can achieve what is needed with Iran and NK, as it already has with Libya.
Incidentally, no, we could not "end up with" those places "more hostile than ever". It is not possible. They already were willing to shoot at us. The only restraints they ever recognized were those created by fear. Our enemies are not restrained by any good will toward us. They are only restrained by fear of consequences - including those in their own internal politics due to people there preferring what we can offer to what they can offer, certainly.
As for "my estimation" and "best bet", it is all argument free. You haven't given the slightest actual reason for thinking a lick of it. Why do you think Iraq is easier to handle without also dealing with Iran, instead of Iraq being easier to handle when a neighboring subversive country with all kinds of agents within Iraq striving for an anti-US, fundamentalist Shia regime is replaced by a popular pro US democracy? Why would it be easier to stop Baath terrorists in the Sunni triangle while they still have sanctuary in Baathist Syria, than if they didn't? Isn't it a bit like saying, "I'm not for this impractical idea of going after Hanoi, we need to worry about just Saigon and Hue"?
At several points you say you are worried about regime change as a goal of policies. Um, supporting regime change in Iran is already US policy and has been for years. It is not like we've all thought the Ayatollahs are the greatest thing since sliced bread, until that whacko Perle came along. The question is what we are willing to do to further that goal, not whether we are for it. We don't want regime "unchange" in half the middle east, because the regimes are godawful. We'd never support these characters and we'd jump for joy if they were gone. The only question is whether we sit around hoping something just happens (domestically etc), or whether we actually do anything in favor of such changes.