I also thought it odd that SUPERGIRL would attend Clark and Lois' anniversary, as seen in the group photo. Most of Clark's aquaintances knew Linda Danvers was a "cousin", though a background check through Midville adoption records might raise questions -- wasn't she supposed to be an orphan?
Sure, but orphans merely lack living parents. It's kind of strange for her to be in an orphanage when her cousin is a well-known and presumably decently-paid reporter, but presumably one Clark was established as her cousin, he covered her upkeep in Midvale.
But why would Supergirl be there? She was never depicted as a close friend of Clark, though she did appear in some old "Lois Lane" comic books.
Superman, though, is a good friend of Clark's and of Lois's, and Supergirl's connected to him. So the friendship clearly happened through that connection, in the intervening years.
They are also family guests, though the other party attendees should be wondering how a Metropolis newsman would be so chummy with a Gotham City millionaire.
Weren't Bruce and Clark established to be friends over the years as well?
I suppose the mark of a great "Imaginary Story" or Elseworld is whether readers still want to the tale continued EVEN THOUGH they know full well it will likely NEVER be part of mainstream continuity. And for me, "Superman Family #200" is one of those very few instances where I'd like to revisit events that "never REALLY happened". Good to know that issue has other fans.

For me, at least, it's not the mark of a great story so much as the mark of an interesting set-up -- I'd like to see more of that future because I'd like to see it explored, but I still didn't think that was more than a passingly-okay story. The cover hooks me every time, though...
kdb