Mine wasn't dodgy and there was white crap on the cap and rotor. Could be b/c it isn't completely sealed from the atmosphere (there's a "valve" if you look closely) or could've been the condition of other components that were installed in there before I got the car.
I know other people have had corrosion under there without cracks in the cap, etc. though, and not limited to civics or Hondas either.
As to the wires, over time the wire inside can break down and increase resistance. Good quality wires will last a very long time but unless you test them with an ohm meter (easy and relatively cheap but most don't) you don't really know you have properly functioning wires on all cylinders, which is why I'd recommend changing them if they're quite old.
Eventually the rubber insulation (newer cars may have HQ synthetic insulation so this is less of an issue) will crack and it's possible that before that even happens that the wire inside is creating more resistance than it's supposed to.
Either way they'll need replaced so if you look over them carefully and test them all then you'll know when they need replaced, otherwise it's not a bad idea to change them as preventative maintenance.
Just because there are plug wires widely available today that will virtually last forever(if taken proper care of), that doesn't mean the ones that come on one's car are of that same quality.
Last edited by A-series; 09-17-2007 at 01:35 AM.