I'll start.
My first BMW was back in 1986. My '74 tii "The Thrasher" that I still drive today.
The first thing I did was remove the mini-lite wheels that came on the car because I didn't like the way that they looked. The paint was pealing and the metal underneath looked sort of grey "like lead". I ended up giving them away along with the original magnesium lugnuts. The rims were 6x13 and made of magnesium, little did I know. I installed 6x14 "bottle caps" instead.
Next, I removed the original "black" coil and replaced it with "what I thought was an upgrade" blue coil. I even remember the mechanic saying it was a downgrade. I didn't care, I thought it "looked" better so I had him install it anyway. He did bypass the ballast resistor correctly, so it was fine.
The next thing was replacing the original aluminum wiper blade holders with plastic Bosch units. Again, I thought they looked better. What a shame. I remember those original aluminum units stamped with "Made in England" and TriCo, and I threw them in the trash.
That's it for me... Next