How much mace to use for a sauce? I am making a quart of sauce and want to use just enough mace that it can be detected. How much should I use?

Is there a general set of guidelines of quantities of spices per volume of sauce?
There are no such guidelines. The needed quantity will be different dependent on all other ingredients in the sauce (both spices and others) but also on the food habits of the eaters. 

The way to get it right is to add incremental small amounts and taste.