I don't think the idea of rebooting Superman was so bad. It probably should've been done in the early 70s, rather than 1986 (O'Neil's run was an attempt at a revamp, not a reboot). I just think that what Byrne did was too radical an overhaul.
I do not want to resurrect the discussion about the merits of the Sand-Superman saga which we hammered out at great length a while back, but are you trying to have it both ways? Denny didn't go far enough; John B. went too far. (?) We really have to have the blinkers on not to see that "Superman Breaks Loose" was a cut-off of the old, and an introduction of the new. The silliness was gone (as much as we adore the Silver Age) and Superman grew up so to speak, ushering in a whole new era for him, beginning with Denny's work. I don't agree everything from Mort's years remained "canonical". Look at what Elliot S! did with Krypto, his updating and re-introduction -- same character, but an amazing transformation into a mature storyline and character. Look at how Luthor grew as a character, and that superb first novel "Last Son". Superman always had natural "reboots" all the way along, and the "Bronze Age" is a great example of a distinct and worthwhile era in his development. Julius Schwartz had it right: he didn't chuck anything out. He initiated a shift, a tweak here and there, an emphasis on this, a push to the background of that... Nothing wrong with Bronze Age Superman. What a great era. Julian has mentioned Len Wein. Some of my favourite stories are his. Look at how he took "minor canon" (Superman's neighbours) and matured it, developed specific ideas. He didn't throw anything away. Why throw things away? I think the Bronze age teams did wonders with a heavy and deep history.