Pards, have you owned or at least driven both vehicles personally and extensively before saying that the Grandia is smaller and "severely underpowered"?
We purchased the Hiace over the Grand Starex mainly because we were looking for a van that had a seating and interior configuration close to the MB100. Seating capacity of both may be similar but our family preferred having no jumpseats to move about in the ingress and egress, and the taller cabin of the Hiace. The Starex may have bigger dimensions on paper but your overlook that its engine is upfront while the Hiace has its engine underneath the driver.
As to power, yes the Starex is far ahead in the power and speed department... comfort as well is a better with the Starex. The Hiace however, in spite of having a low HP rating on paper, is nowhere near underpowered and is also quite efficient given the size its carrying. It has the power to pass on two lane highways up north and to ascend mountain roads without having to shut off the a/c or ask you passengers to breathe in. If you're familiar with the Tagaytay Midlands to Highlands road, it can take it at full load with the a/c on, on second gear all the way up; same goes when you're on Kennon road (Camp 6-7) where you only have to take it on 1st gear on the hairpins unless you want to throw your rear passengers around.
We're thinking of changing the GL Grandia to a Starex already though as we don't need much passenger space anymore and would suffice in a 7-8 seater van for our family's use.

I still like the imposing, boxy design of the Super Grandia though (in my taste).
* the Super Grandia, leather for me as well. Panget ng hubcaps nga.