While we both agreed that Lost Cities has been superseded in our own experiences, it's place as the go-to couples game/girlfriend game/ room mate game/ etc seems to be still going strong.
Personally, I would rather reach for Morels or Jaipur or Battle Line, just to name a few. Lost Cities no longer interests me but boy did I play a ton of it in years past. I can't think of a lot of games that got as much play for me.
While it is now the poster child for the style of game, Lost Cities certainly didn't create the niche. I have absolutely no idea what game you could give credit for doing that. I can see arguments for games like checkers, which means that casual two-player games go back to the dawn of time.
The worlds of two player games is a different than multi-player ones. The games that you play with only one other person are different than the ones you play with a group.
And it is such a diverse world as well. Classic abstracts like Go or Chess, not to mention the vast majority of modern abstracts. Two player war games are the rule, not the exception. And that's not counting casual games like Lost Cities.
My own world of gaming has been increasingly focus on two player games. I may not be playing Lost Cities right now, but in many ways, it has become my guiding light.