Although I am neither a fan nor an expert on lowering Vanagons, I do have some observations to pass along. The lowest stock Vanagon production springs were on the Carat models, so some Vanagon owners seek used Carat springs to lower their vehicles. As a rule, Vanagons are 15 + years old and often with 150k or more miles,so you can't expect to find springs that aren't suffering from fatigue. This leaves us with H&R springs and Weitec springs. As important as which spring you select, it is equally important which shock you choose. Shock selections include KYB, Bilstein, and Koni. Here follows my input on the subject, but I welcome other peoples input to help fill in the blanks, which I will add to this discussion.
springs-- I'm not a big fan. Lowering a car always sacrifices some
comfort or suspension travel and I think the H&R's go too far by
going too low and losing to much suspension. Paired with the KYB's the
ride is horrible and even paired with Bilsteins I find the ride
unpleasant. If you have smooth curvy roads the handling is very good,
but maintenance of roads is no longer the priority it used to be so we
are all too often plagued with potholes, bumps and uneven pavement
which make for a particularly unpleasant ride. The only time I have
driven a Vanagon with H&R's and not been dissatisfied with the ride
was when they were coupled with Koni adjustables. The Koni have
adjustable rebound. There are 4 settings and we found the 2nd to
stiffest setting to be best. The adjustment is done with the shock
removed from the van if you choose to experiment, but at least in the 2
wheel drive model shock removal is not too taxing of a task.
- Weitec springs -- Weitec springs are made in Germany and are a popular choice there. These lower the Vanagon more than the Carat springs but less than the H&R's. Right off the bat, that is preferable, as you at least still retain more of your suspension travel (and don't lose as much ground clearance). I have driven these with Bilsteins and got what I was expecting. Nice handling at speed on turns, but the ride was a little worse than stock (bouncier) when the road was not smooth, but it was acceptable. The best ride of all is combining the Weitec springs with the Konis. The Konis have adjustable dampening setting which can be set on the stiffer side and compensates for the reduced suspension travel to provide a more stable ride.