This is a great thread. I am conscious of the weight also and would love to shave 100 lbs or so and get closer to the E46 M3 weight. The mods would have to be tasteful aesthetically and fully reversible though.
I wish it were possible to get identical front seats, but fully manual and without any motors. Also, does anyone know how much the BBS sourced(?) concept wheels for E90/92/93 weigh compared to the stock 19s? I would love to save 12 lbs there if possible. Exhaust would be another area I would consider, but I like the sound of the stock setup. I wonder how much weight EDC adds? I don't see how it could be that significant.