I have no dog in this hunt, so I am going to let go on what I think.
Personally, you have to look at what started everything before anything else can develop. You have to include some cars not mentioned such as the original Corvette. True, this was not a barn burner, but it was a platform that could be built upon. The '55 shoebox with the smallblock. It was the everyday car that put the chev smallbolock on the map. The 409 Impala, a big car with grace and speed. The Z16 chevelle, the '67 Z/28, the ZL-1 camero, and the LS-6 Chevelle and Corvette. All of these cars are without a doubt very important cars. Dealer cars are a a different bag of chips.
For me, the most 'significant' Chevy is the one in someones garage that they would rather part with their first born than that car. If it was not for the passion that is ignited within on these cars, then Chevy, Ford, Mopar would not have developed the car for the 'enthusiast'.
Oh, by the way!
