Actual math
Note: throughout I used the KBB dealer trade-in value for a typical car condition extrapolated out 3 years. This is because RedShirt appears to want to keep trading in vehicles. I also assumed that RedShirts numbers from the first post were exactly correct (owe exactly $15,000 on the Caravan at 2.4% interest for example).
Option 1: Do nothing for 3 years
Keep the Caravan, keep the Forester.
* You now have a Caravan worth $11,500 + a Forester worth $6,500. Total value: $18,000
* You paid 36*$400 = $14,400 in interest
* Lets suppose you pay $1000 more in maintenance (RedShirt's numbers from post #50).
* Your Caravan would still have a loan with a $1203 balance.
* Grand total: $18,000 - $14,400 - $1000 - $1203 = $1,397.
Option 2: Trade in the Forester for a 3-year $200 Civic Lease
I assume you take the current KBB Forester value of $12,000 and pay down $12,000 of debt for the Caravan.
* You now have a Caravan worth $11,500.
* You pay $3,049 in remaining loan payments to fully pay off the Caravan.
* You pay 36*$200 = $7,200 on the Civic lease.
* Assume that on a 5000 mile / year vehicle the extra insurance payments for a new car basically are a wash with the small gas savings from going from a Forester to a Civic.
* Grand total: $11,500 - $3,049 - $7,200 = $1,251.
Conclusions:
So, on the surface, you are $146 ahead by doing nothing after 3 years even with the extra maintenance. But, there is a major catch that car dealers try to gloss over for leases. In option 1 you have 3 more Caravan payments and then you own both vehicles free and clear. In option 2, you either need to buy / lease another car or you have to pay $12,000 to buy that Civic. So, in option 1, your monthly payments go away for good for as long as you are happy with your cars. In option 2, you are right back into getting a $12,000 loan or another ~$200/month lease. Meaning if you take option 2 and look out say 5 years, you are now 24*$200 (additional lease payments) - $1211 (final Caravan payments) = $3589 behind because you needed another lease. Sure, lets say you need another $1000 of maintenance, but you still are WAY behind in the 5 year timeframe if you lease now. By leasing now, you are trapped in the continual upgrade cycle unless you can come up with that $12,000 to pay off the Civic.
The concept that buying / leasing a new car now is ever a way to save money needs to die.