I think your spray bottle method is pretty cool, and I see the benefits you mentioned. I have to go along with the other post about fine tuning CO2 volumes though. CO2 volume is a big contributer to everything else in a beer, even appearance. Being able to precisely dial that it, not just to style, but even to one specific beer, is pretty vital if you are striving to get a beer from Very Good to Excellent or World Class. All things being equal, a small change in carbonation can make a noticeable difference between two otherwise identical beers. Same as final pH, same as mineral content, same as ingredient freshness, bla bla bla. So, imagine the brewer who weighs his grain to the ounce, hops to the gram, and measures ph to the second decimal point, but then ballparks his CO2 volume to within about a half of a volume... The beer may be awesome, but not exactly the same each time. Therefore not exactly at its best every time.
Cool idea that works, just hard to be very precise.