So how many little fixes have you had to do to your BMW? For a typical owner each one is likely $3-400 plus actually going to the dealer. How much more has the Sienna cost in that case? For alot of people, even just a single $1200 trip to the dealer is much better that three $400 ones...
Also at some point the Sienna became a N.A. only vehicle (needed to be big and cheap) which may have indicated Toyota was really trying out a broader cost cutting strategy on them including parts suppliers? Most guys I know either go Grand Caravan on the cheap, or a used Odyssey for minivans and most do fine once the Caravan gets some decent brakes.
So far on BMW in 42,000 miles (bought car with 80k), I had replaced the gasket on the oil filter housing, and this gasket on the fuel pump (mind you, this is a universal design with a supplier that supplies to other companies, including Toyota for the same part).
On Sienna I had to replace:
2X brakes, with 3rd set purchased but sold the car (will sell parts on CL).
Struts and shocks were purchased but decided to sell the car (Again CL)
Master cyl.
"Fixing" (basically, just aligning rear liftgate, still could not close it using the button): $300 (Toyota quoted $3,200).
Now, take into consideration that Sienna had 85k when it was sold, and BMW has 122k and I track that car. Actually, I upgraded struts and shocks for track purposes on BMW at 105k and one shock was showing some weakness (it was tracked, OE shock) while struts were going strong regardless of track abuse.
Also, I DID work on SIenna. Master Cyl. replacement on Sienna would not be below $500, and you can calculate brakes, struts, and shocks, and that is not counting hinges that are as strong as hinges on my drawer in the office. I am not sure why do you think the Toyota dealership is cheaper? They wanted to charge the spare tire 3X over what I paid for BMW X5.
Now, I did a lot of upgrades on BMW suspension, for the sake of upgrade, bcs. it is worth it.
Now, I listed some time ago all the fixes I had to do on Prado.
Also, one thing, on Toyota, there are some things I did not bother to fix. I upgraded audio on BMW and took down probably 6-7 times door panels to adjust speaker wiring etc. On Sienna, I had a rattling window when increasing volume (JBL) but I just could not make myself take down the panel. Kind of the same way when you don't bother to fix some appliance part in the house. Just not worth it.