Can you give a real world example of how you are doing this? Why don't you just get a lease? Essentially this is what you're doing except you're self financing the lease.
I'm also on the new car train except that I drive the car into the ground. Once it starts needing repairs more frequently, I ditch it for a new car. This means that I will hold a car for about 10+ years, 150K miles.
Leases can come with some horrible upfront fees and some horrible turn in fees, plus mileage caps and higher insurance. Plus with this method I have full control over what I want to do and how long I will keep the car, if things were to suddenly get bad financially, I'm under no contracts with the car and no hidden fees, allowing me to keep the car longer than intended if needed and save more money. The goal is to eventually get to a point where I buy the car cash up front (though every time I go in now they always want to throw 0% finacing at me, more than happy to keep my lump sum in savings or invested, especially when you can get the "cash buyer" rebates easily thrown in with the 0% rate with just a bit of haggling and pushback.
Heres what I've done:
First new car:
2008 Honda Accord: Bought new with 215 miles on it, Paid $23,000/72 month loan, maintenance with oil changes included for first 5 years (dealership program). Put down 5k, 72 month finance (2.2% rate). Drove it for 5 years to 58k miles. Trade it in to dealership for 12k (had it fully paid off early by paying extra toward principle each month).
2011 Hyundai Sonata SE: Bought new with 8 miles on it, Paid $10,000 after trade in with 36 months financing (0% rate). Drove it to 37.5k miles, needed new tires and the schedule maintenance were going to cost $1500, said screw it and traded it in for $16,000, it had been completely paid off.
2014 Hyundai Sonata Hybrid Limited - Bought new with 12 miles on it, Paid $9,000 after trade in, with 24 month financing (0% rate). Free maintenance till 60k, Currently driving this one and at 20k miles.
Basically the idea is my payments have always been around $250 - $350, its the range im more than comfortable paying, and all except the 2011 had its maintenance pre-paid in the sale price (excluding tires). When I trade this one In I'll buy my next car with its trade in money and only take out a 12 or 18 month loan (if not pay for it upfront if I can put enough in my car fund by then). I plan to drive this one to 60 though, so should have another 4 years on it at least, which means I'll be going a good 4 years without a car payment and no worry about major maintenance thanks to the car being under a bumper to bumper warranty the entire time I own in.
Like I said its not cheap, but once your in the new car system its easier and easier to get value out of it and stay in it.
