Indeed. A more expensive policy is cheaper than forking out for a new car, and on top of that, they can also refuse to cover a third party claim against you.....which if you end up seriously injuring someone (or worse), then you really are up a creek without a paddle!
You could play the ignorance card - "It was like that when I bought the car and didn't know any different, I don't know Golfs" - but even then there's still no guarantees.
Declare EVERYTHING, even LED bulbs, changes of switches and AC panels....EVERYTHING!