If you haven't refinanced your home in that 3 year time, I'd also look at doing that. Rates are so low right now, you should be able to get a 15 year loan with payments a hundred or two over what you're paying now if you have a 30 year.
I wouldn't worry about putting 50% down either, not with vehicle loan rates where they are at. My biggest thing is just not being upside on the vehicle when you drive it off the lot, usually the trade takes care of that and more, but if you don't have one, put down enough to make sure you're never underwater, small down payment plus taxes and tags.
09 135i 6MT, ZMP, PPK1
13 X5 35i ZMP, ZMX, 2VA
13 Tiguan SEL 4motion