See, to me, a sleeper is based on THE CAR, not the engine. It's a car that's a lot faster than it looks. And, seeing as how small blocks fit in A-bodies just fine and big blocks fit with a little massaging, I'm never SURPRISED that one is fast, but then I'm a Mopar guy, and I've driven Darts for 25 years, so maybe some kid in a Civic might not know any better, in which case it's a "sleeper" to him.
I also think that there are two kinds of car guys: The guys that hot rod their old cars and only pull them out of the garage on the weekends (and drive a NEW car or truck to work all week), and then there are the guys that wrench on their cars and drive them as primary transportation. I think there are more slant guys in the latter category than the first. Those whose hot rods are "toys" won't be much affected by gas prices, while those who drive them every day may eventually have to break down and become a weekender. So I doubt higher gas prices will really help slants TOO much.