I`am Peter from The Netherlands and I have an Opel Omega Stationwagon the sister of the Catera.q
This was the car when I bought it
First changed the wheels.
Irmscher Sport Star 8" x 18" with Michelin Pilot Sport 2 235 40 18"
Then the radio
The original radio
The navigation radio with color information display and cd changer and the original Bose Sound System (not pictured)
The navigation radio and replace all the switches (Opel Vectra facelift model)
This is what I did on the outside of the Omega.
And change the interior from textile to an leather sport interior
Did some more things but you are not allowed to put in more than 15 images.