I think the year you're looking at is okay for the most part. I've got an '01 I bought with similar mileage a few years ago, the drivetrain has been pretty solid, but everything else is crap. The rear hatch leaked and the carpet got mildew so I had to tear it out, the "premium" factory JBL stereo had 2 tweeters blown before we bought it, the rear power windows only work sometimes, the power sliding doors are a hassle they need to be reset every few weeks, often during the middle of a rainstorm (thank goodness I don't have carpet anymore,) the front driver's door handle cracked so it couldn't be opened from the outside, the clip on the front passenger's door handle broke so the rod that engages the latch was dangling and the door couldn't be opened from the outside. I've got the dreaded P0420 code, which basically amounts to Toyota goofing up the programming of the ECU and ignoring it since it only affects vehicles that out of the emissions warranty. Gas mileage is 20mpg at best, often closer to 15mpg if there's any city driving involved, I think it's got excess power except at 2k-3.5k rpm, where it falls on it's face. The injectors are pretty noisy, the dash rattles, the fan belts squeal often, the brakes feel a little weird some times like the system is burping, power steering at idle can feel heavy. I don't care for the traction control system, I'm not sure how it works but it feels like it applies the brakes rather than locking the differential, it may work better on AWD but with FWD it doesn't seem to do anything.
In it's class the sienna is still one of the better options. All of the domestics have serious drivetrain issues at or before 100k miles, Nissan and Kia/Hyundai are gas guzzlers and have some drivetrain issues as well, the only real competition is the Honda, but it too has transmission problems depending on what year you're comparing it to and the seats are the most uncomfortable seats in any mini-van I've driven. The Sienna isn't a bad choice, but the whole mini-van platform is a compromise as far as reliability, durability and quality of materials and workmanship go. I'd say a middle of the road SUV is better in those aspects than the best mini-van.