How about this for an idea...
One of the ways to increase power is to advance the timing and it should improve fuel encomony I believe. The obvious problem is pinging. Choose the grade of fuel you want to run and set the timing to stock setting and then advance the timing until it starts to ping and back off a bit. Higher octane fuels resist pinging so depending on how much you drive it may not impact your fuel cost much at all since it's less than a $5 difference for a full tank.
Also, if the engine temperature is cooler I believe you can advance the timing a bit more before it starts to ping. A lower temp thermostat might be an options and a product like Purple Ice or Redline Watterwetter might lower the temperature a bit.
I'm working on tuning mine back to regular grade fuel and I'll be putting some Waterwetter in in the next couple of days to see what it does, if anything.
Just an idea...
