We just bought a new 2005 Sienna 7 passenger XLE and we love it so much. Have you checked out the forums in http://www.siennaclub.org
yet? Tons of information, and those folks are very obsessed with their Siennas.
For us, the most important thing we learned on those forums was the manufacturer's loyalty program which you negotiate separately with the manufacturer. You can search for "loyalty incentive" to try to find the thread. My dh got a generous check from Toyota using the information on that thread.
But in addition they have other information, like what is a good deal in your area, endless information on each and every option, etc.
We checked the Odyssey first, because our Civic was perfect for five years and we just prefer Hondas. But the Toyota had a much smoother ride, and that's what we wanted because our dd gets carsick very easily.
We got the XLE because I wanted the automatically sliding doors. I have two kids 22 months apart and it was hard to struggle to the car to get the doors open and shut in narrow parking spaces while carrying one child, holding the others hand, and carrying groceries. It's also horribly, suffocatingly hot here in Texas in the summer and I like opening both doors from a distance to give the car a chance to cool off before I get there.
Have fun. Be sure to check out the incentive program on those sienna club boards. You might get a cash windfall that will surprise you.