Toyota Sienna, any owners with practical info about them?

I just receved a letter from the Dutch government and they are increasing the roadtax on my Volvo V70 AWD diesel from 2000euro to 2300 euro next year (close to 2500US$)
There are years where I pay more in roadtax than in fuel (1.4$/liter diesel, 1.8$/lieter petrol/gas), which means getting something cheaper in roadtax can use more fuel and still be less of a strain on the family budget.

I came across the Sienna and it looks very nice.

One thing I never got is why the second row in American people carriers have only 2 seats. I have 3 kids, so would always need to keep at least one seat in the third row up...
But the Sienna 8 seater has a solution. But does this tiny middle-insertable-third-seat work or is it just an emergency solution?
And how is the 3rd row seat? I rang Toyota and when talking about a people carrier, they adviced the Prius Plus. (Officially the Sienna is NOT sold in the Netherlands and somehow they did not advice the people version of the HiAce or whatever toyota Van that IS sold here). Cool, but they go for as much as a Sienna on the second hand market* And the third row seat is OK for my two smallest kids, but I can't see me driving 500miles with 7 people + luggage (let alone the dog) in that.




* when I say the Plus goes for as much as a Sienna, that is comparing Dutch Plus prices to German Sienna prices. But before I get the Sienna on a Dutch license, I will need to spend some extra tax (yes, tax again) to get it on the road here (cars are taxed with anything from 10 to >50% of net value here when they are first sold by the dealer, but this also goes for imported cars. You can get part of this money back when you EXPORT the car, meaning that thousands and thousands of secondhand cars are exported which in turn drives up the price of our entire second hand market. You have got to love our government).