As an owner of two Siennas, 1999 and 2011, I wouldn't want anything customized on that vehicle. The 1999 maybe, but that was first-gen, back when Toyota was still interested in launching something that didn't fall into the category of total econobox crap. I loathe my 2011 for the cheap way it's made and its legendary poor handling. In a rare moment of restraint, Consumer Reports described its handling performance as "lackluster". That's way too generous. Even under a light load distributed toward the rear, the Sienna wants to fish-tail. It doesn't track well. I've tried different tires, I've had it re-aligned more times than I can count, both at the dealer and at independent providers. It doesn't matter. The lackluster handling is just part of the deal. There's no reasonable workaround that I've ever found.
The next obvious question would be, if I dislike it that much, then why do I still own one?
Because our money has gone into our Class B. Both my husband and I are living with crummy daily drivers so that we can have the financial freedom to invest in the vehicle we like the best.