I've never really thought it was all about gravity. I usually think about it more from a dark verse light decision. I will keep dark beers like porters and stouts in starage for long periods of time because they develop very nicely over longer timeframes. High alcohol beers will also age well but I do not keep light colored beers in storage for long periods.
Not really scientific but it has worked for me.
Some light or lighter colored beers can benefit from extended aging as well. Consider a a lager like Samiclaus or some of the Belgian styles. Gravity is one of the key factors for choosing which beers to cellar, though it's not the whole picture.
Good points and I agree completely. I haven't really brewed beers like those (yet) so I wasn't thinking that way.