I think your correct about the "Ain't broke don't fix it" I woulden't mess with it until you start getting erratic engine problems that don't usually happen. I have an Alpha trainer that has about four gallons through the evolution .46 engine and I have never replaced the glow plug yet. I also have an HPI Savage monster truck that has the original plug in it and it has more than 4 gallons on it also. The hardest part of a glow plugs life I believe is in a brand new engine or if you tend to run an engine very lean.......I think.

Hope this answers your question.

Joe