My assumptions are quite reasonable. Here's my assumption, it's an assumption: I think Iran took down the drone to show the West that it has capabilities to jam its radar and equipment, and the ability to take control of our weapons.
Yeah... That's a stretch.
Jammed it? Could be. But hacked the code and took control of it? Really? I also don't see a threat to the US Mainland from Iran's littoral navy, whatever they may claim they can do.
As for why is Iran giving us the finger. Cuz they can? Cuz they have nothing to lose? National pride?
As you point out, an invasion of Iran would be a disaster. I even disagree that we could "win" whatever that means. Iran would be much more difficult that Iraq, and we can hardly claim we won in Iraq. We're stretched and our economy is broken. (Osama Bin Laden may have paid with his life, but he clearly accomplished his objectives theer)