Hi, just came across this as I was googling Lunar Spider replacement. My 3rd pair are getting a bit long in the tooth. Really frustating when Nike mess around with their ranges. I used to run in Pegasus before I went more lightweight, but even those changed year on year.
In terms of Nike, probably the closest are still Lunar Racers, although I find them a bit wide, not in fit, but in general flappiness if that makes sense, they're just not as sleak as the Spiders, but I am using them as my second pair at the moment. Again, Nike tinkered with them and not for the better. Have also liked Zoom Streak in the past, even managed the marathon in them, although my feet weren't happy by the end.
Really hope Nike do a Spider LT4, will buy many pairs!