Yesterday I had so much fun flying my 49 inch Sureflite Cub on an old OS 20 that starts instantly with a flick of the prop, and throttles and idles perfectly. The sound was not very loud and everyone seemed to like it. Most of my flying was low, close in stunts at about 1/2 throttle, occasionally bumping it up for a turn or a roll, then back down again. I used about 3 ozs of fuel per flight. On half throttle the engine sounds great. Call it "nostalgia" if it makes you feel better, but I wouldn't trade that sound for the nasal wheeeeee of an electric for anything. Also flew my 4 Star 60 with an OS 70 FS that sounds fantastic at any throttle setting.
To answer the question of the thread, I think nitro is on the way down, judging from the newcomers who fly electric, but not out. In our club about 80% of the new guys bring electrics, but at any given time at the field the planes in the air are at least 60% glow.
I'm amazed at the disappearance of the .09 to .30 size glow powered planes. They are just tremendous fun. Their electric counterparts seem to be taking over that niche, but not a one of them holds a candle to my glow powered planes in that size.
Jim