I use this 'i don't know anything for sure' attitude to remain open to possibilities that fall outside what science can currently measure at all.

I think that should also be the correct scientific attitude and I my personal opinion based on my limited experience is that that's how a great deal of the scientists look at it.

In the end, there is nothing that can be demonstrated with absolute certainty, but the degree of certainty that you might expect from a particular theory should also be taken into account.

Germ theory was once preposterous because we didn't have the instruments to measure them.

Preposterous is a judgment based on intuition. Intuition has a lot of value when hypothesizing, but it should be excluded from the evaluation of correctness.

The more important thing is that when it was proposed, it was not unreasonable to view it as unsubstantiated by evidence as the evidence was not in yet. Keeping in mind that looking at the theories that have survived scrutiny gives you strong selection and confirmation biases.

Look at it this way. When germ theory was initially proposed, there were let's say 9 other theories to explain the same phenomenons that have now been shown to contradict the evidence. But before the evidence was in, you wouldn't have had a good way to distinguish between the 10. So saying that all of them were not substantiated at that time is not at all unreasonable.

Of course, I'm speaking a bit hypothetically here as I'm not actually aware of the exact history of germ theory, I'm talking about the principle.

Additionally, it's always possible, especially if you go further back in history, for particular scientists or even whole scientific communities to have been reluctant to accept new evidence even when it was clearly contradictory to the then accepted theories. My personal opinion is that it is less likely today, but again it is more likely in some branches of science than in others.

Just because these things don't exist within our physical reality doesn't rule out the possibility to me that they may exist in other dimensions... dimensions which may have no physicality in the sense that we experience it at all.

Sure, we cannot rule out anything that is untestable, but the question here would be how reasonable would it be for us to base our views on such unfalsifiable claims? There are just too many things that are theoretically possible and if we have no way to peer into them reliably, should we postulate them as reasonable?

Humans might believe in myths because they had technologies to peer into some other reality, but keeping in mind the utter diversity and inconsistency of myth, is it reasonable to assume they did?