I think that one point that has been overlooked in this debate is the assumption that the Iranian govt is acting as one unit, i.e. Ahmedinejad and Khamenei on the same side. There are reported to be deep divisions between them and the Revolutionary Guards are not under A's control.
The increasing sanctions (soon to be added to by the EU) will put greater pressure on both A and K and will most likely give rise to increasing public unease, perhaps rioting.
I can't pretend for a moment to be an expert on military hardware (or software, for that matter), but I strongly believe that the most important battle (as far as the US and Iran are concerned) is psychological. The Iranian leadership is clearly under pressure domestically; totalitarian dictatorships generally deal with unrest in two ways; brutal suppression (which they're quite used to doing) and trying to focus attention on a foreign enemy, i.e. the US; the trouble is with the latter, that if you're going to spit venom and then do nothing, you only weaken your position domestically. This is why I think that we're in a new environment here; Iran's position, together with the imminent US election campaign means that the situation has changed significantly.
With regard to the small fast craft, these are clearly a threat, but in order to prepare and arm them in sufficient numbers to pose a threat, this would be seen on satellite imagery and I have no doubt that the US has satellites covering pretty much the whole of the Iranian coast, from Iraq down to Pakistan, together with air bases and other installations. Would they really be able to put together the numbers they need to pose a threat, without the US being able to anticipate an attack?
I don't see Israel attacking Iran; I think that it recognises the changing situation and if it could, it would probably like to provoke an armed conflict between Iran and the US; how to do it is the question! Could it intercept/ "amend" Iranian military codes to bring this closer? We know what it did with Stuxnet ...
I do believe, however, that we are entering a new and very dangerous phase in the simmering conflict between Iran and the US.