I don't see anyone bringing the issue of the engine durability. To my understanding the original engine is designed for particular CR that creates given load on piston, connecting rod and crankshaft. Increasing CR I believe will increase the engine performance for sure, but at the same time it will increaso the load on these parts that may cause premature engine failure.

I wouldn't try to squeeze every bit if HP from "garden" engines - they are not designed for that. Something's gotta give. I would rather focus on the engine reliability running gas-glow plug combination. To increase the spped of flame you can use nitro, for detonation prevention - higher grade of fuel. For engine timing - the grade of glow plug. This is my understanding.

I have one thing to worry about tho. Did you guys experienced low lifetime of the glow plug running gasoline/oil only? Some time ago I run my engine on regular gas/oil mixture keeping the glow plug on the battery all the time, but the glow plug failed after about 20 minutes. Did I have bad luck or there is an issue there?