I think what you're trying to say is smaller subs don't look as impressive to the uneducated eye; mainly because of all the teenage hype about 15s and rapper's showing off their 15" L7's and singing about their Alpines "in da trunk." I know what you're saying though.
In regards to what I see on a regular basis, I personally am more impressed by other factors. If I see two flashy plastic cone subs labeled with "xxxWATTS Peak" in big letters sitting in a pre-fab sealed box I probably won't be impressed. If I see a Wal-Mart amp unmounted with a tangled wiring mess I'm probably not going to be impressed either. If I see a brand I know nothing about I'll get curious and probably do a little research to see if they're gold or garbage. If I see somewhat uncommon, but often liked equipment brands such as "DD, Sundown, Audioque, Fi, Audiopipe, Image Dynamics, etc..." I'll likely be impressed. By then end of the day, the size of the sub really doesn't mean much to me. If you're trying to impress people the first thing I would do would just be to make it look nice. Mount your amp, hide the wires, and dust your stuff off and you're much more likely to get a "wow" from just looking. At the end of the day though, untrained eyes are often impressed by shear size, so yes, in identical setups, when showing highschool kids, without actually turning it on, yes, I would say a bigger sub is more likely to impress somebody.