Over at thesamba, there's a thread on "upgrading" the vanagon booster to
BMW model that is larger diameter:
http://www.thesamba.com/vw/forum/viewtopic.php?t=443880&highlight=brake+booster+dash

And, viewing other threads over there, it seems several of their forum
members have done this, seeming satisfied with the results.

Has anyone hear made the change?

I ask because I think I may have to replace our booster, and the BMW
booster's price new seems to be about half that of the vanagon booster.
(e.g., here:
http://catalog.importrp.com/item.wws?mfr=ATE&sku=BMW018726&source=GOOGLEBASE
)
(I'm not interested in installing a used booster.)

My understanding is that:
1) maximum braking power won't be improved, as this is limited by the
calipers and hydraulic system, not the strength of my legs at this point.
But:
2) the power required to achieve any given braking power will be reduced,
so the brakes should be more "responsive" in that sense
3) otherwise there don't seem to be major downsides.

Obviously, I'm especially interested in any thoughts/feedback on #3.