I spoke with a mechanic today who suggested lowering the pressure within
the cooling system as a means of putting less stress on head gaskets ...
perhaps more for ageing gaskets that are more susceptible to developing
leaks.

He postulated that the pressure would be significantly reduced if the
coolant temp was lowered by putting in a cooler thermostat (by not much)
and by causing the radiator fan to kick in at a temp. ten degrees cooler
than it does stock.  He claimed that the only downside might be a slight
reduction in fuel efficiency.  He is a smart guy pretty knowledgable
about vanagons.

Is this an old already rejected theory?  Wouldn't running the engine say
10% cooler...or any cooler than stock set up, have some adverse
consequences?