I see your point, but don't you think that using the LS7 would make just as much sense as using the LSA, to a certain degree? While we can debate about whether 470 torque and 420 torque are a 'stone's throw' from each-other, I don't see the difference between using the two power-plants as it relates to the Camaro.
Logically, if the Z28 is using the LSA then THAT version of the Camaro SHOULD draw buyers from the base 'Vette, right? Probably not as much as you'd think. They are completely different cars... and while I see your logic that the Camaro being in a second, visually appealing package coupled with a back-seat might be 'added benefits' that lure buyers, I think the Corvette appeals to a narrow segment of the population and its nameplate alone draws customers (as evidenced by the fact that LS1 Camaros and Firebirds were nearly as fast in a straight line, and still sold, but so did the 'vette). The cars DO compete... if what you're looking at is straight line performance. HOWEVER, the Corvette is a vastly superior setup for track applications... and if you are craving a higher dose of HP than a standard Vette but also want blistering cornering, the Z06 is an excellent platform for that.
I suppose the essence of my point is that GM using the LSA or LS7 both make sense... and I could easily see them churning out an LS7 version of the Camaro to out-do the Mustang Laguna Seca edition, etc. After all, the LS7 is known to have a more difficult time with boost (in stock form) than the LS3 or LS9. It can be a BEAST with heads/cam, though. In fact, I think many of the people who like tuning N/A motors might be drawn to a 7.0L COPO Camaro that was slightly less expensive than the Z28. Do I think they'll do it? Probably not... but mostly because, for the small segment-gap in price, it wouldn't be efficient to do R&D on a 6.2L SS, a 7.0L "COPO" or similar, and the 6.2L supercharged LSA Z28. I agree with you that they likely won't use the LS9 as that is reserved for the flagship car, though...
By the way, I'm terribly sorry if I misunderstood your point. I'm exhausted and running on very little sleep