I don't think it's got anything to do with any of those options. Assuming that the sailors had violated their waters, and they were seized on those grounds, and also assuming that the sailors were not engaged in blatant espionage, it would be standard procedure to capture, interrogate, and then release them after a few days.
That said, I think there's a very deep game being played over Iran, and I don't have all the answers, but a couple salient facts that I think need to be kept in mind:
1) Russia, China, Venezuela, and Brazil all have significant ties to Iran. War with Iran would anger those countries and unleash retaliation from them on any country that attacks. Whether that would entail military or economic retaliation, or both, is hard to say. Thinking only about China, should they stop trading with the United States and should they dump their dollar reserves, it would hurt both us and them, but they're prepared to take that hurt. We're not, and they are waking up to that fact. We could not withstand a combined military assault on our positions in the Middle East by China and Russia while simultaneously enduring the loss of Venezuelan oil and the loss of Iranian, Russian, and Iraqi oil from the world market. China has the cash reserves to outbid us. War with Iran will cost us far more than most people understand.
2) If we're just talking about stealing oil for Western Corporations, there's considerable uncertainty about whether the juice is worth the squeeze. Iran may have a lot of oil, or it may not. There's quite a bit of information that their oil industry may fail by next decade.
3) Bush co. hopefully understand that a serious enough pretext has to be found to start war with Iran so as not to incur the wrath of Russia and China. We're shopping for that kind of pretext because geopolitically, if we can take Iran with little consequence, we will be the last man standing as we slide down the backslope of oil production starting this decade. Russia's got plenty of oil left (more than we do) but their land area is much larger so it takes more energy to run industry. More than likely, Russia will effectively fragment (whether they appear to politically or not). But if we could get Iran to do something really stupid (like sink a carrier or blow up an embassy), China and Russia will not be able to credibly oppose any retaliation.
4) As a close corrollary, it is almost certain that both Chinese and Russian intelligence is working actively in Iraq, Iran, and Afganistan to prevent us getting that kind of pretext. Watch the news in the next few months for rumors that Russia had something to do with this release; it'll merit a passing mention on CNN or BBC news. You can then dig into the alternative news for the full story. That full story will most likely be that the behind-the-scenes dialogue included some kind of ace-in-the-hole that Russia was holding that would weaken this as a premise for war, while at the same time showing that Iran had little cause to continue to hold the sailors.
5) Our intelligence in that area of the world continues to be pretty bad. There is no imminent revolution in Iran. The only revolution taking place is a cultural one, and it's quite a bit more tame than most would like to believe in the west. The people are not about to rise up and overthrow the Ayatollah.
6) All that said, we may still go to war with Iran without a pretext. If we do, it will not necessarily be a blunder, depending on specifics. Geopolitically, and assuming we don't have to worry about such silly things as having human empathy for the people doing the dying, going into Iraq was the right thing to do. The Saudis needed the oil to mask the failure of their Shedgun and Uthmaniyah mega-projects and the rapid decline of their oil production, and we needed a police station closer to the center of the action. Iran is another story. They're selling oil in Euros and are considering Yen and Yuan, which will ultimately have the effect of crashing the dollar if they can make it stick for a while. Additionally, continuously increasing production constraints worldwide will make conditions very, very bad before too long. Right now, the effect it's having is that third world countries are being priced out of the bidding, freeing up the oil they'd have otherwise consumed for first world nations. That game cannot continue forever, though, and our leaders understand that. Taking Iran would solidify our hold on the Middle East, and would ultimately control Saudi Arabia when the time comes for that.
As for what Iran wants, Oldreliable more or less nailed it. Iran is not a bloodthirsty nation any more than we are; if their oil industry is failing, however, they have a motivation to get western powers out of the Middle East. They'll have managed to resurrect the Persian empire if that happens.
