I have two virtually identical P-07s with ProGrade kits installed. One is for CCW, and the other is for practice--live and dry. I'll probably pick up a spare sometime, but meanwhile I have enough spare parts to maintain mine.
I also have a bunch of Gen4 9mm Glocks and spare parts for them.
I don't have spares or full parts kits for niche guns that I only carry occasionally: G43, G20, LCP, LCR.