Folks I have known with boilers do just as you proposed. They run rooms they are in at a normal temp, and the unoccupied rooms around 10 or so degrees cooler. The claim of cost savings with split duct A/C is based on this premise. Condition the room you are in, and spend less energy on the others. I wish I had a boiler instead of forced air. A co-worker just replaced his 40 year old boiler with a modern one and said he cut his gas use by 25-30 percent.