Hitting the drive-thru may save a few precious minutes, but what you eat could save thousands of dollars in the long run. When it comes to a vehicle's residual value, it's what's on (or not on) the inside that counts.According to the results of a national survey conducted by Kelley Blue Book Marketing Research and Taco Bell Corp., nearly 60 percent of all vehicle owners eat or allow someone to eat in their vehicles, yet only 34 percent rank a clean interior as "the most important attribute to the long-term value of their vehicle" (vs. 66 percent for exterior). And that could be costly."Our research highlights a huge misperception among consumers: that the interior condition of a car has less importance than the exterior appearance in terms of residual value," said Jack R. Nerad, executive editorial director and market analyst for Kelley Blue Book. "Cars in excellent condition and appearance -- both inside and outside -- can be valued thousands of dollars higher than those in good or fair condition.""With people spending more time in their vehicles, the number of dashboard diners has also increased. The dirty little secret? Messy interiors could potentially cost owners thousands of dollars when it comes time to turn in or sell their vehicles," adds Nerad.The Kelley Blue Book Marketing Research and Taco Bell survey found that people who allow eating in their vehicle were less concerned with their vehicle's overall appearance, ranking all vehicle attributes lower than those who don't allow eating in their car. Some other highlights of the study include:--Burgers and fries are the "messiest food they have eaten in their car" (34 percent).--A combined 90-plus percent of respondents indicate auto body(72 percent) and exterior paint (19 percent) are the most important attribute to long-term value of a car, compared to just five percent who named an interior part as most important.--When given a choice of 13 attributes to rank in importance with regard to eventual resale value, stained seats and carpets ranked as number 10 and 11 (respectively).