guess Ether wont ruin glowplugs, its destroying your enginge when too much of it gets in 1 cylinder and due to a glowing GP it misfires ..just like when you have a glowing grime nest in your gas engine...and it fires the gas/air mixture too early (like when piston is goin upwards) and thats too much force on the engine...some parts may fail & it will be destroyed.
Mostly GPs get ruined when glowed too long or when it wont start up good and you dont wait a bit before crankin/glowing again. And of course when they take to much voltage / amperes for some time...
the "magic spray" is just something that fires up really really easy.... and thats the Problem with Diesel engines: In a Gas engine the Ingnition is timed by the spark plugs, and even with another "fuel" for example ether ..its timed right.
in a Diesel engine the "ingnition" is timed by the pressure the fuel/air mixture gets when the piston goes up: and with Ether its another, so if your unlucky it could fire up even when then piston has not reached its "upper deadpoint" ..and here we have the "misfire" problem again. much force on every component of the engine..not good