No, your 1, 2 or 3 don't help at all. If you see the elves or detect them, then they are not "invisible, undetectable elves", and your observation has no bearing on the truth of the sentence. So the sentence absolutely cannot ever be tested, cannot be said to be true or false, and therefore is in some sense outside the domain of logic.
You can have a separate argument about whether an untestable statement is necessarily "meaningless" (maybe the way it makes you feel is the meaning) but I believe the only point the author is trying to get across here is that some statements make predictions about the world, and some don't, and it's worth being aware of the difference.
You can have a separate argument about whether an untestable statement is necessarily "meaningless" (maybe the way it makes you feel is the meaning) but I believe the only point the author is trying to get across here is that some statements make predictions about the world, and some don't, and it's worth being aware of the difference.