If you're happy with your current gap, keep it. The wider gap requires additional voltage to get a spark to jump across. Higher voltage = higher spark temp. Higher spark temp = more efficient burn + probably a smoother idle.
According to the engineer I spoke to, cracked insulators on PROPERLY INSTALLED PLUGS is caused by the wire core heating, expanding & rupturing the insulator. This can be a result of a gap too wide (less likely) a plug wire/wire boot failing (most likely) or a failing coil (pack) (somewhat likely).
His strongly recommended solution was to check the coil pack & replace if needed, replace plugs & plug wires at the same time & narrow the gap if the problem is persistant - which it was for the gents I was trying to help.
Again, if you're not exploding plugs, keep things the way you like them. I certainly don't like for people to spend money if they don't have to.
