I have a strong history of tinkering with any vehicle I've owned.
Your shout.
The A5 is the first vehicle that I really don't want to make significant changes too. Audi did a bang-up job out of the door;
Here here
however there is still some room for improvement.
Not sure what?
Factory Air Filter is always made from paper which is very restrictive and over the long-term cost of ownership, expensive. Changing that out for a K&N not only makes financial sense, but performance sense as well. Allowing the engine to breather easier and produce better HP and increasing fuel efficiency.
Evidence?
Wheel Spacers. The Rims on the A5 S-Line have been voted as among the Top 10 wheel designs in the world. Why leave them tucked into the wheel well!? Even Walter de'Silva's original design sketches had the wheels flush with the lines of the body. By properly pushing them to the intended design location, you are returning to the designers intended location while also improving the handling.
If they are Y spokes IMHO they look cool as they are (Thanks)
Regular incandescent light bulbs vs. LED's for interior lighting. One of the most stunning parts of the A5/S5 design is created with LED's on the front of the car. Audi recognized this in part and attempted to carry that to the interior by placing LED lamps in the foot-well. Why not in the entire interior of the car!? You are finishing what Audi intended to do, plus it provides a "cleaner" and crisper interior light.
Evidence please.... who said Audi 'intended to do'???
These are only three cases which I submit to you for consideration. If chosen carefully the Aftermarket can assist in returning the car to what Audi intended to build, but for whatever bean-counter reasons, changed their path on. Compliment the design, don't trample the design.
Agree with the final sentence but do not agree with 'buggering up' pretty decent standard kit...
Humble thoughts.