Interesting perspective, and one that I agree with: a character's history is the single most important thing about them, both in creating future stories and showing how they're characterized. Some of these "historical" stories were just gut-wrenchingly powerful. I doubt any story that involves the introduction and description of life on Krypton would be as suckerpunch powerful as what Jerry Siegel did in "Return to Krypton."
It would be a very heroic decision for DC to make if they said, "you know what? All that stuff from 1986 on? It really happened. Let's get to telling more stories." Not just because Superman comics past this point were by far the richest kind of comics world ever created (everything from Supermanium to the Kryptoniad, the Epic Poem of Krypton) and because these stories have additional resonance as being "the way it really happened," but ALSO because history itself is worth preserving, is worth making useful.
It's very wasteful that they have all this history, all these ideas from 70+ years, all these stories they could tell sequels to...and they can't make use of it because of an arbitrary reboot point.
You are right that the Earth-1 and Earth-2 dynamic DOES feel very retroactive. However, I think they were able to get away with it, because Superman comics until the 1970s did not quote from or derive from the past; previous battles were not brought up or used to affect current characterization (the exception was with Gardner Fox, who took his superhero history VERY seriously; the JLA had statements like "Gosh Manhunter, we haven't teamed up together since the battle with Starro!").
I would become a softy. Lois Lane would suspect that I was vulnerable to marriage, and spend an entire comic series trying to convince me of it. I would begin to seek out a "Superman family." So I think the most pivotal part of the story, that differentiates between Golden and Silver Age versions of myself, could be the sudden arrival of Kara.
This is a pretty good idea. It explains the change in Superman's personality in a natural way. Though one problem is, Superman didn't have to take responsibility for Supergirl. Superman chucked her in an orphanage; it wasn't a THREE MEN AND A BABY deal only with a teen.