How long is sugar (mixed with minor ingredients) good for?
They're good pretty much forever. There is not enough available water for things to grow in there. Mind you, the more aromatic and subtle parts of the flavor will dissipate over time. 

The sugar absorbs water, giving the combination a very low water activity, meaning there's little water available for microorganisms to use in growth.  As long as your flavoring pieces are small and well mixed with sugar they will not spoil.