I was contemplating this the other night, while giving the Xmas Cake its last feed before marzipaning it. Didn't come to any conclusion, but 'accidentaly' spilt Drambuie onto the offcuts, and decided that you can't over-feed it .
OTOH I once tried feeding a different sort of fruit cake, and gave it so much to drink that when we cut it we discovered that the marzipan had dissolved!