RE: Why did VW increase the tire pressure recommendation
in later models?  Any reason I should not run higher pressures (the
tire max is 65psi) than what is on the door sticker?

Speculation is that over the years VW found that higher pressures were
better (stability and wear) or were paraniod about safety but had
recommended lower pressures early on for percieved comfort.  But that is all
speculation, no source of facts on the subject that I've ever heard of.  And
the weight of the Vanagon and Vanagon based Westfalia campers did not
increase that much over the years.
And no real reason to limit pressure to door jamb numbers IF the max
inflation pressure of the tires is not exceeded.  BUT watch the tire wear,
your best indicator or proper pressure. You might search the archives for an
old thread on 'The Mustard Test' for a means of checking for proper
inflation.  I know a very experienced Vanagon owner/driver that runs several
pounds above the factory pressures on his Hakka's, higher when heavily
loaded, with no problem.  Based on my limited experience you will be able to
notice just a few pounds difference in harsness of ride and handling
especially if running lower pressures.