With anything as old as a Vanagon, the mileage is largely irrelevant.
What matters is what sort of care and maintenance it's had over its
life, and what its current condition is.

About the only thing that will destroy a chassis is untreated rust, or
a severe collision.  Everything else can be repaired, replaced, or
maintained as long as parts are available and the owner is willing to
spend the time and money on it.

Allan