Changed my insurance recently from 2005 Audi A6 1.9tdi to 2003ML270CDi which I believe is several insurance groups higher. The cars have a similar second hand value.
The additional premium (Privilege Insurance) when up by £19 for the remaining 7 months, and then I increased my annual mileage from 10k to 15k they upped it to £33 instead of £19.
On the ML they asked if it had any mods, I said that I wasn't aware of any other than factory fitted, but then went on to say that it had sat nav & side bars. This did not affect their price but these two mods are now listed on the insurance schedule. I didn't think to mention othere factory fitted extras - auto for example - as this comes up when they type in the number plate.
On the Audi, I had always thought it sat a bit low (I bought it as a pre-registered car, 1 month old & kept it for 3 1/2 years) the mud flaps would regularly catch on speed humps, etc. When I sold it the buyer told me that it had sports suspension!!! The supplying dealer never told me - where would I have stood in the event of a claim?