You don't want the customer to get drunk!!!
Also, the flavor should be diluted to give a mellow suggestion of alcohol. An undernote if you will.
Alcohol, something tells me, may break down the tender structure of your cake if not the cream filling.
When flavoring syrups, you want to have enough alcohol to smell and taste without falling over.
I like to use 70% syrup 30% alcohol or coffee. For flavor pastes and oils, measurments vary.
Kirschwasser is used in a classic preparation of Schwarzwalder kirsch torte. But, then again, most Germans don't seem to mind getting a little drunk. We served it at the German restaurant I used to work at, there didn't seem to be any noticeable breakdown of the cake itself, but I'll check with the pastry chef there as I am certainly no expert.
hmmm. maybe that's why the tortes that we brush our liqueors directly on the layers are our best sellers.... i have found no breakdown of texture or loss of moisture- i was concerned that i was missing something technically important
ps thanks for all the imput on the dacquoise/japonaise/jaconde inquiry