Thanks for a great response. Reading it reminds me of the #Brexit referendum. A complex topic with many facets boiled down to a binary yes/no. Never ends well
To elaborate, at least in my case the car I have is a 2005 A3 2.0T with 78000 miles on board. It’s been serviced properly throughout its lifetime at Audi using OE parts, oil etc. Additionally with some exceptions we’ve always used Shell V-Power for fuelling. The car has had no emission issues/smoke problems and flies through MOT, including no service advisories in the last one. In terms of fuel economy, the car has always been consistent: when driving in city, which is were it gets 80% mileage from (I’m in London), we get around 24MPG but that goes up to 46MPG when doing motorways.
Given the age and mileage of the car, I’m looking at preventative measures that will ensure longevity of the engine and fuel system. Any additional benefit derived, e.g. quieter engine or increased fuel economy would be a plus for sure.
Hope the clarification was useful and apologies for the original almost useless question.