You are correct...The ZL1 is as you say worth at least twice as much as the Z28. The problem is, how the ZL1 is being perceived on line.
Maybe I need to do a little more research to find out how the First Gens progressed back in the day. Did GM do the same thing back then? Jumping from the SS straight to the most powerful of all First Gens, the ZL1? If so maybe there is still hope for the intermediates. If this is true there is still time for the rest of them to be developed before the dooms day date of 2016...