Well im not sure if 30% causes the motor to wear quicker or not. what i do know is that you want about .021-.025 inch of squishwhen you run 30% nitro. put some solder through the glow plug hole and turn the motor over. be sure to not get the solder in a port or anything. just run it up against the side of the sleeve. measure it with some calipers and remove or add shims under the button to get the correct squish.
The other thing i do know is that the more nitro you put into the motor the cooler the motor will run. sounds funny i know but follow this logic:
say you mount up your motor on a Dyno. you first run say 20% fuel through the motor. you tune and achive the best power that you can which registers on the dyno as 2HP. (remember these are just theoretical numbers used for this example.) you also note the temperature the motor was running at when you achived this number. it runs at 250 degrees. A little warm, but acceptible.
Next you run 30% through the motor. This time you tune to achive that same HP number, 2HP. you note the temp and it reads 210. This is because of the extra nitro. it cools your motor.
so in a race tune, you can achive more power with 30% than 20% at the same temp.
as for a plug...im not sure. It sounds like the motor is modified and that can change the charecteristics of the motor significantly many different ways, and each of wich could reqiure a different plug.