The Magnaflow sounds great but regarding performance - maybe ~5hp - nothing you would actually feel.
And I've never heard that a new MAF would make more power on this car. Maybe you confused the MAF with the throttle body?

My recommendations for more power:
No 1: CAI (from TVT oder Needswings) or the larger CLK airbox with K&N's (for the stock look)
No 2: ecu tune and larger injectors from TVT
From those two (actually three ) items you'll get IMO the most bang for the buck.
If you want to spend some more you then could go with the 74mm throttle body or an exhaust (maybe a true dual design) or the thermostat or the polished intake manifold or... But these parts don't add as much hp as the CAI and the tune.