There are some great bakers on this board and I hope they can help. While I do bake a lot from scratch, some of my favorite cakes are "doctored" beginning with a boxed mix. For years I have made a very rich, "gives-you-a-headcake" doctored chocolate cake (cake mix, pudding, sour cream, choc. chips, etc.) - no Kahlua added. A few years ago I cut out a very similar recipe to what I use EXCEPT it added Kahlua. So for the doctored boxed versions I don't believe leaving it out hurts one bit - you won't have the coffee flavor of course. I hope someone will answer for you regarding a scratch cake.