I tend to agree with this point Nigel. But it doesn't take away from the truth of your earlier point that we are trying find lines of sight when faced with what may be a small fraction of the objects that could be part of any such line. Particularly if the objects may not only be no longer there (like a wooden structure) but also may never have been "fixed" to the surface in a way that would leave an archaeological record (like a deliberately placed human pyramid, for the sale of argument).

If we come up with the speculative proposition that there could be a goblin in the well, doesn't it make sense to consider why the goblin might have been there (i.e. what the possible motivation is for a goblin being down there)? I agree that you will not necessarily prove anything at all, but it's a natural consequence of considering the possibility of the goblin being there at all, I think.

So, the statement "there may be a goblin in the well" can naturally be followed with the question "what makes you think that?" or "why would a goblin be in the well?". Possibly a question about the "why" may help to discount, as well as corroborate, a theory about the "what". There may even be a further supplemental question like "how could a notional goblin get in the well?". Answering this question may also disprove the notional goblin speculation, for example if the answer is "it's scientifically impossible* for a goblin to get in that well" then you don't need to go any further with the "there may be a goblin in the well" theory, without needing to go a climb down the well to investigate. :-)

*Of course, this is subjective in itself!