RE: Electrics killed 1/2A?
I think you're totally right that electric is killing off 1/2A and having a goodly poke at the 15 to 25 size market to boot. The prices of a motor and pack are pretty comparable to the cost of a good 1/2A engine these days thanks to the flood of cheap product coming out of the orient.
It's only the old school that grew up with the smell of castor and the scream of a 6x3 in their ears that really has a love for these little jobs. Sure there's one or two newcomers but for the most part the new small model flyers are going electric. And if they got bored of their models then they would have been bored of a glow model as well. The glow fliers are the ones that are totally addicted and won't ever kick the habit so it's no wonder that those flying small glow are continuing.
As for your glow plugs don't worry. The community here won't ever let you stay down for long. I suspect that if there's two of us left and one guy burns out the second to last glow plug in creation that the other 1/2A guy would take a plug out of his second engine to give to the first guy so that they could each fly until the next one burns out and then they'd take turns with the last plug in creation until it too burned out. So if you need a plug to keep flying then just ask.