My question about IC is why someone would design a machine that would have parts not essential to function?
The only thing I could think of were safety guards etc. You can remove them and the machine still functions, but someone could get hurt.
In any case, IC is circular in much of its reasoning. It does not anticipate increments in ability to function.
Some parts are not necessary for function, but make the machine more efficient, like the front sights on a handgun.
To be even more specific, Michael Behe (the main IC guy) would agree that if handguns were like bacteria, they could probably evolve their own front sights, but they couldn't evolve something irreducibly complex like the semi-auto loading mechanism, he would say that must be the result of design. (in the case of a handgun, he'd be right, of course)