They're strictly for looks for 99.99% of enthusiasts.
As for using OEM M3 front setup, we tried that on my car but it didn't work. Something about how the M3 control arm not mounting to the knuckle? I can't remember. Maybe someone more technical can chime in for me.
'02 ///M5 Imola Red / Imola Red '09 335i Alpine White / Coral Red