How can we definitively tell if the vacuum over there has the same energy density as the vacuum over here?
Further, how can we tell if the energy we think we find in vacuum here isn't energy that arises from particulate contamination? Or, for that matter (ha) is coming from somewhere else? Has someone managed to (a) create a perfect vacuum and (b) measure its energy and (c) determine that whatever was measured as appearing at X, definitely hadn't disappeared from all the possible Ys? Somehow, I doubt it. If for no other reason than our access to some of the other Y (say, around Andromeda) is... limited. As well as non-contemporaneous -- if something disappeared from that region, to appear here, we wouldn't have any indication it had happened for about 2.5 million years. And even then, our ability to measure vacuum precisely at that distance... not so good.
My (admittedly not very deep) understanding of vacuum is that it is defined by a lack of content, and that a perfect vacuum would be defined by a perfect lack of content -- and were that simplistic idea correct, then I don't see why how much perfect vacuum there is has any bearing at all upon the total amount of energy.
And, if vacuum is indeed empty when perfect, but we think there is energy detected in what we consider a perfect vacuum, then perhaps we're simply misinterpreting the goings-on within an imperfect vacuum. Perhaps there is more to get rid of than the molecules and particles we know of at present.
Or, perhaps space is infinite and at least somewhat plastic to start with, and our situation (going with the idea that the space we can observe seems to be expanding) is more like adding a thimble of water to a planetary ocean (let the ocean conceptually be infinite for the sake of an example.) Perhaps space over there is contracting, while space over here is expanding.
My own position is that any cosmological proposal that includes the phrase "arose from nothing" or similar is probably better filed under astrology until actual evidence is found of the idea -- not possible precursors or echos, but an actual example of what is being described. We seem to be pretty clear on the idea that matter and energy are essentially interchangeable, and we have no experimental data that proves stuff arises from non-stuff, so at least at this point, I see no reason to take an assertion of "arose from nothing" seriously.