I have an 06 Montana SV6, with about 80K on it right now. Aside from oil changes and new pads, I had a strut bushing replaced, and a steering column (under warranty).
I think they are actually pretty good. For $15K, I would say it's a good deal.
A Sienna or Odyssey will hold their value better, but you got to look at it in absolute terms as well. i.e after 3 years if the Odyssey depreciates 30%, that's 10K. If the Uplander drops 50%, that's 7.5K. Plus, you will have less interest charges with the GM (given smaller principle, and likely lower interest rate).
There's disks all around btw, at least on the Pontiac.
Actually the Sienna's are not holding their value very well in comparison to other Toyota's. One of the poor performers for Toyota that way for some reason. Maybe because of competition like this?
And I saw an entire auto carrier of new Uplanders heading towards Kamloops a couple of days ago. Must be moving if they are shipping them.