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But given the "it's thriftiest" explanation provided for this "very clean" genome, I think it raises a number of very significant questions with regard to why other genomes have accumulated so much apparently random stuff, if there is some genetic advantage to be gained from this streamlining.
The thing that comes to my mind is: maybe that "random stuff" isn't really random after all, but simply serves some purpose we haven't discovered yet.

Well, at least some of the random stuff has been proven to be useless to survival. They bred knockout mice, where the knocked out regions were noncoding regions of no previously known function. The mice were indistinguishable from normal mice. I don't know if they ever tried to breed a line of mice from those knockout mice, so I don't know if there are any long-term effects to knocking out that particular line of junk, but it's still rather compelling evidence that much of the noncoding sequences really ARE junk DNA.

Some scientists have speculated that pseudogenes, at least, form a junkyard like those in Junkyard Wars: They provide lots of ready-made subassemblies that can be pressed into service later on.

Then there's the rationale I've thought of for having junk DNA: When a gene duplicates, it gets plopped down in a (presumably) random spot on some chromosome. If there was no junk DNA, then the chance would be 100% that the duplicated gene would "crash" into another already-functioning gene, most likely disabling it. With 95% of our genome being junk, there's only a 5% chance that a gene duplication would disable a currently functioning gene.

So when a genome acquires the capability to produce stretches of junk DNA, it's actually acquiring a buffer zone that acts synergistically to vastly increase the viability of gene duplication as an evolutionary tool.

I think the JennyP Theory of Noncoding DNA explains why most single-celled organisms don't have junk DNA while all(?) multicelled organisms do.

Some scientists have speculated that pseudogenes, at least, form a junkyard like those in Junkyard Wars: They provide lots of ready-made subassemblies that can be pressed into service later on.

I tend to lean in this direction. It seems to me that G-d isn't doesn't leave a lot of extra stuff laying around for no reason. Perhaps they had a function in the past that was superceded by changing needs and/or conditions. DNA is truely wonderous stuff, and a very efficient way of storing a lot of information.

I don't know if they ever tried to breed a line of mice from those knockout mice, so I don't know if there are any long-term effects to knocking out that particular line of junk, but it's still rather compelling evidence that much of the noncoding sequences really ARE junk DNA.

OTOH, how many times have we recently seen announcements about scientists who've discovered that sections previously thought to be junk, were really used for something?

It seems more than a bit premature to speculate that what we don't understand is "junk until proven otherwise."

As for the JennyP theory, that's part of what I was getting at: if there's a forcing function toward "thriftiness," it seems that the accumulation of "buffers" in the middle of a genome shouldn't happen.