Ye tell your insurance company about your pedal boxes 

Why wouldn't you? Whilst it's not something that gives more power, I have absolutely no doubt that if the insurance assessor clocked it whilst looking the car over, he'd have it noted as an "undisclosed modification" which I'm sure they'd try to use as a way of getting out of paying any claim.
Whilst it doesn't add any more power, it
could be seen as something that does make the car faster due to a quicker throttle response, therefore they would maybe either increase the premium or (if they won't insure modifications etc.) not quote for it. It's not just about the insurability of the car, it's about the perceived risk of the driver - if you want to make the car feel faster, they might assume that you're the sort of driver who drives faster?
Either way, I wouldn't give them any excuse whatsoever to attempt to wriggle out of a claim. In the eyes of the law, without declaring it, you're simply driving round without insurance.
Whilst (many years ago) I've had undeclared cosmetic mods on cars (through ignorance of the way insurers work) I wouldn't miss out anything nowadays - simply not worth the risk.