I can't buy that it's rational to commit suicide by taking others with you, even if the others may be entirely made up of the enemy which, of course, is not the reality. Tying the rationality of the act to a subjective level of effectiveness seems...irrational. I can understand the impulse but not that it is arrived at rationally. IED's better serve this end I would argue, but don't require one's suicide. Remember the old adage 'It's better to run away today and live to fight another day' - that seems rational to me.
On the specific example, IEDs are often made out to be simple things. In reality, creating them requires quite a lot of knowledge, and doing real damage with them is difficult. It's not for everyone.
On the general concept: living to fight another day assumes that you believe that things will get better, if you're being rational about it. That's not a likely scenario. It might have been in 2003, but not anymore.
I'll grant that deciding to fight for anything may be considered irrational, but the moment you have decided to fight, it is impossible NOT to conclude that you will most likely die (if you fight the US) and so you should consider suicide attacks as a reasonable option.
Another thought regarding the removal of the occupiers - how does this square with the London or Madrid bombings, or even the Oklahoma bombing by McVeigh and crew?
London was just a case of "fighting them there so we don't have to face them here". Perfectly rational. Suicide was part of it for many reasons. Surely it was easier than figure out exactly how to time these bomb, especially through the unpredictable traffic. Also, a suicide pact may hold up better through weeks of preparation.
McVeigh was a veteran of the fist Gulf war, disenfranchised and in with the wrong crowd. There are likely to be many like him over the next decade. Since they can bide their time and have good prospects of inflicting mass casualties without having to die themselves, they don't go for suicide attacks.