I agree, it is a great addition and one that I'd never read.
There are some fantastic concepts in this story, just begging for more detail. For instance, Superman travels forward in time to the far-flung future of 2000 A.D. (beautfully drawn by Wayne Boring) and people there obviously know who he is - his great exploits are described in the history books and there is a museum devoted to him - but where is the Superman of 2000? Did Superman die? Leave the planet? Retire to the old-folks home? What eventually happened to him?
One answer that I know of that was given to this question was Elliot S! Maggin's explanation that Superman left Earth some time at the turn of the century - yet another great example of good writers respecting their characters and valuing the stories of their predecessors.
