I'm also on the fence.
Why tint: Recently I've been having a lot of people pull up along side and try to race. Would be nice to just be incognito inside.
Why not tint: I've got a pretty unique combo in Sparkling Graphite on Bamboo Beige. The colors just pop when you see the car. Tinting the windows would definitely take a way from that.
Current: 2008 BMW M3 Sparkling Graphite/Bamboo Beige/6MT. 1999 BMW M3 Techno Violet/Dove/5MT. Next: 2017 BMW M3 CP