coffeeking, I think you need to look at it from the insurers point of view. They would be asking why have you removed those items from your car, which presumably was perfectly servicable in the first place.
Insurance companies are far from being idiots – even if the person you speak to on the phone very often is, so why pretend that you’ve stripped your car for reasons that are nothing to do with performance?
As far as adding a full roll cage to a car – it’s not difficult to imagine why you would do that, so have a guess what would happen to the premium.
Remember, the insurance covers the people you might crash into as well as your own car and is an assessment of risk – if you are stripping you car and making mods like roll cages then the risk of insuring you suddenly increases massively.