In 2011 I paid $52K for a new S4. I believe the North American production was ~8000 (US and Canada) per year. There were at least 6 companies making high quality catback exhausts and several companies making catless headers (I had EuroCode long tube). Plenty of suspension parts, I had KW V3s coilovers. Lots of tuning options and let’s not forget VCDS for customization. But, more importantly there are a large number of independent shops that actually know how to work on these cars. Maybe I was lucky, but I found some really knowledgeable people that did great work (mods and maintenance) on my car.