Just passed 326,000 mi. on my Sienna. Purchased new in 1999 - absolutely the best car ever! Faithful maintenance seemed pricey at the time-timing belt every 60,000 miles, e.g., but I stuck to it & can count the number of repairs on one hand. Water pump at 200,000, stuck seat belt, tie rod ends @ 250,000. Had 3 prior Chrysler minivans, none of which lasted more than 140,000; all needed new radiators, transmissions etc. Inconceivable on this van. Not even broken plastic parts. Didn't use the tow package 'til recently. Added a trailer hitch and took a full U-haul across the Appalachians at 300,000 miles w/no problems. Driver seat has great lumbar support - when my back hurts I go sit in my car.
Reliability. Stability in rain and snow. Great visibility out all windows. Safety - rear-ended a couple of times, but bumper had great shock absorption.
Gas mileage could have been better. But it hasn't declined much as the car has aged. At 326,000 I get about 21 mpg on the highway. Best I ever got was 23 or 24.