For me, the Z3M Coupe is the one that got away - I turned down a 60k mile silver S50 MC in 2014 because I thought I could find a better example for my 7.5k GBP. There were two others for sale for 8k at that time, and I didn't realise that was the inflection point for the market. In the end, I bought an S2000 just before their prices started to climb.
I looked at the M6 GC as a family car, but the rear seats were a little impractical and my wife wanted an SUV. In other circumstances, we might have almost matching garages!