There isn't enough info on differences between 2012 MY 535i and 550i. If we talk about 2011; it was obvious that BMW was subliminally encouraging customers to buy the 550i over the 535i. The msrp shows a $10000 difference in base prices but when one looks deeper, it is clear that the 2011 550i came with many more desirable standard features eg navigation, leather upholstery, ambient lighting, park distance control, 100% chrome grill etc. There is $5000 worth of standard features. This means that the net cost difference is only $5000 and it is worth it to attain the mighty 550i engine.
The 550i is not just faster from a stop. It has far better passing acceleration in the important bandwidth 25 - 70mph. This is very handy when overtaking an obstructive truck on the highway.
Cosmetically the 550i looks better. The trapezoid exhaust tips give the car balance. The cylinders in the 535i look too skinny for the car!