I agree with what has been said here. Get the M3, low miles, extended warranty. If need be, sacrifice on a option or two, in exchange for less miles.
As for gains, a good tune and drop in filter/scoops can get you /- 30 whp. You can probably get close to that with a catless xpipe or better yet a full exhaust. Tune filter exhaust= hold on tight.
2011 E93 - Space Gray - 6MT/Silver Novillo/
OE Tuning/Gruppe M Intake/ACS Springs/Vorsteiner CF Type I Rear Diffuser/Textured Matte Black Custom Powdercoated OEM 359s/Painted Reflectors/Matte Grille, Hood Vents and Side Markers/Arqray Race Exhaust/MS Pulley