Yeah was about to say there's already a thread.
Coilpack cover - I doubt the plastic cover would make any difference while they're working. Might extend their life one extra week over the course of a decade And if they're stuffed/on the way out, just having the cover off won't help, cos it's the electricity arcing out to the block, the heat has already made it's impact. The trouble is knackered coilpacks is that it can be hidden (to a degree) by reducing the plug gaps, making arcing just a little less likely. But it reappears eventually (caryard did this to me when I bought mine).
I'm thinking about a new set of spark leads too, see if it fixes up the occasional miss at idle (and across the revs too, I bet).
btw: to test for coilpacks being stuffed: remove the cover, wait til night, find some quiet road, warm the car up, do 4-5 HARD accelerations (hard LAUNCH isn't important, revving out IS, you want boost and engine heat), then pull over somewhere without streetlights, pop the hood, look into the engine with your head directly over the block. Against the dark of night, you should be able to easily see the arc jumping... just don't stick your head too close hehe