I think you've got to figure out your annual automotive costs. Add up depreciation + anticipated repairs and maintenance + insurance + gas + taxes and fees + interest you're paying or not earning on the true value of the car. That's how much poorer your car makes you per year.
True value of the car will be the kelly blue book or Edmunds value of the car (what you can sell it for). Depreciation will be that value minus the value of your car model one year older with one more year of your miles on it.
Your payments are actually irrelevant for this check.
Compare your annual automotive costs with those for a more affordable vehicle; say a $4k Civic/Corolla/Xa/Xb etc.; preferably older with low milage. Note that for a cheap car you own outright, you don't have to pay for collision insurance, so your insurance number would get lower. And any of those cars should cost you under $1k a year to repair and maintain, even if you're putting on high milage.
In short, you probably will end up saving some money by going to a cheaper vehicle. If your current vehicle is a VW Golf, maybe you'll end up saving ballpark $2.5k a year.