"Their harmonies in the seventies were pretty impressive"
I've been listening to a couple of unreleased 70's gigs where the harmonies are competent, but nevertheless very sparse and rough sounding, vs. the Rainbow gig which has always had studio quality stuff thrown on the top.
They were good, but they weren't that good, and it's not really a coincidence that they sounded mysteriously way better on the one filmed gig that they had notions of releasing/screening/whatever.
It's not even a problem that they overdubbed stuff; I for one was just exploring what their thinking might have been when they were doing it.
"They sound better that way. Plus, it's not as though it's some kind of tampering"
We have the albums for that.
"which is valuable in and of itself"
As a historical document, maybe. What might've been more valuable to me was a high quality, unfucked recording of Queen in the 70's.
I bought Rainbow and I love it, but it's a cock-up to stubbornly hang onto those overdubs. It's Brian May saying to my face, "meh, I don't think our audience is smart enough to know the difference".
It's a tad haughty for me.