Performance enhancements for a m104? If you have a degree in mechanical engineering, electrical engineering, or are a certified master tech crew pit cheif for NASA and ALSO feel like spending insane amounts of money you can add a super charger for about another 20 horses.
Plus you can say bye-bye to everything that makes your car a functioning, reliable Mercedes.
But seriously though. You can get the cold air intake, some exhaust, maybe ECU upgrades and that's about it. I'd say with the 1,500-2,000 you'll spend you might get 20hp total.