Originally Posted by NoM3ForMe
If you are the primary bread-winner, keep the car. If you aren't, keep the car.
Seriously, don't let your wife be the thing that makes you walk away from owning your dream car. The S4 isn't worth your time. Inferior looks and inferior performance, FTL.
This guy says everything I would have.
If you downsize/grade to something else (S4..etc) whilst acting on the ideas/emotions of another, you will surely lose. You'll be reminded of your unsatisfactory decision every day until you inevitably get back into an M3.
If it is your money that you are spending (and you can afford it comfortably), keep it. If it is her money that you are spending, ask for a bigger allowance.