yes a cover is also on my project list.. have to stop the water getting in there in the first place as they don't dry out naturally very well or quickly as the plug leads ALMOST seal the hole.
Gaps have got wider using modern electronic systems, the old coil or magneto systems often needed smaller gaps. I think wider gaps offer better or fatter spark with a good electronic system and better burn characteristics than smaller gaps. Also pays to check on even new plugs out of the box as they do vary!
I wouldn't leave plugs in for more than a year, wouldn't necessarily change them but keep them 'moving'.
