Yeah, this is pretty much what I suspected, and I agree with you here (mostly). From a scientific perspective ID is pretty useless and meaningless in "proving" anything. It ultimately all traces back to epistemology, which is, properly, philosophical. I'm not so sure that spiritual things cannot be measured, though. For example, the Bible gives certain criteria for determining whether a person is "worldly" or "holy". Such things could be used scientifically if so desired. It would be sort of like measuring the effects of the law of gravity to determine it exists. I think it's more just an implicit assumption that spiritual things are fabricated.

So say that I'm a completely objective observer (not that anyone really is or can be), would you say that the primary reason a person ought to accept evolution over ID has to do with testability (i.e. evolution "tests" more true than ID does or even can)? Or could it be reduced to a matter of opinion?

This was quite useful, thank you.

I've heard this said before, but it's not immediately obvious to me. Do you think you could give an example?