need help really urgent

hi i am in kinda wierd situation. my dad bought 2003 chevrolet malibu ls sedan fully loaded with cassette player, rear spoiler, leather and sun roof in 2003.it was used of about 5005 miles. my dad spend about 15k in the car and the loan has been paid. two days ago we recieve a letter from the chevy dealer about exclusive buy back used car event. in the letter they worte that due to current incentives and high demand for used cars we can get an 05 chevy at a reasonable price. we are thinkin of tradding malibu for 05 malibu with 3.4L V6 or 2.2L4cylinder. i have heard many people say tht V6 gets better milage then 4. i have also read some decent reviews of new malibu. whay do u guys think?? should we trade the car and get an 05 or stick with 03. this offer ends in five days so i really nedd some suggestions fast. all help will be appreciated.