> I was thinking of replacing the thermostat but I thought of two advantages
> with a cooler thermostat:
> 
> 1. The heads would be at a lower temperature.
> 2. The thermostat opens up and lets 'heat' (albeit lukewarm) to the
> passengers straightaway.
> 
> Does this make sense?
> Are there any disadvantages?
> 
Yes. Slow warmup means more engine wear. Oil is meant to be over 
180f to aid in burning off combustion by-products, and is designed to 
lubricate best at this temp range.

If I'm not mistaken, most cars, including the Vanagon have the heater 
loop separate from the thermostat, so coolant runs through the 
heater core(s) ALWAYS. Just took ours out today in -5C temps, I had 
heat from the heaters in about 5 minutes, although the gauge had 
still barely moved.