Keep the van.
Do the math. A van that is paid off costs you nothing (except for an occasional repair bill) and it gets 18-20 mpg.
Say you drive 10K miles a year
At 18 MPG that's 556 gallons of gas used.
At $3.55 a gallon that's $1974.00 to drive 10K miles.
Instead you go Lease a Yaris that gets 35 MPG. Great news right, WRONG. Do the math.
$2000 cash down
$1548.00 ($129.00 x 12 months)
10,000 miles of driving
At 35 MPG that's 286 gallons of gas
At $3.55 a gallon that's $1015.00
Add the $1015.00 to the $3548 (the cost of the new car)
and it costs you $4563 to drive 10K miles
Even if you took away the $2000 cash you spent for the down payment and assuming that your van would need $2000 worth of repairs every year it would still cost you $2563 a year to drive a fuel efficient car.
Tell me how is that saving you money? If you break it down by the month you're spending $295 a month (car payment + cash down) to drive a fuel efficient car that saves you $80 a month on gas.