Philosophical Speculations

Does Dark Matter exist? We observe only its gravitational effects on regular matter and light.
Therefore we infer that it is matter. But wait. There are other theories, for example Modified Newtonian Dynamics,
that suffice to explain what we observe.

Further observations are needed to confirm which, if either, theory is correct.

But wait. Why do we need to observe phenomena at all? If all is consciousness, why do we need
to act as if there were a reality apart from consciousness?

Why, indeed, are there laws of nature, properties of space-time, and hidden realities
of which we are not aware at all, waiting to be discovered?

What of life on far distant galaxies beyond the light horizon, forever hidden from our view?
Does our inability to observe them, mean that, they do not exist?

Are there other universes, other "existences," of which we can never know?
Can they exist and yet be undiscoverable?

Would not hierarchical models of reality account for them better than Monist Idealism?

Finally, what effect (if any) does our asking these questions have on reality?
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Would not hierarchical models of reality account for them better than Monist Idealism?

Monist Idealism does not exclude hierarchical models. It's only the Bernardo's version of idealism that is "flat" and has only MAL and physical universe with no layers or hierarchies in between, but the reason he does that is that he wants to present the most simplistic, naturalistic and parsimonious model and stay away form assuming the existence of directly unverifiable levels of reality. But it does not have to be that way. We are free to assume and include in our own idealistic models additional hierarchical layers, Deities, "discarnate" realms of dissociated existence and so on. There is an overwhelming evidence (from mystical experiences, NDE, regression therapy and so on) that those realms indeed exist.

Finally, what effect (if any) does our asking these questions have on reality?

They have little effect on understanding what the reality is, but have significant effect on understanding how it behaves and help us to develop our science and technology. Science/technology is a practical tool and can be very useful as long as we do not take it religiously. The fact that we can meet and exchange ideas about idealism on this forum is a result of the centuries of progress in physics and technology, and I think we should have at least some appreciation of this fact.