Normally when I make a cake, I use one of the extender recipes from this site. I was wondering what would happen if I use the Enhanced Cake Extender Recipe and replace the water with milk. Do you think the milk, sour cream, butter, and extra egg would cause any problems with the cake?

I would think it would make it more rich and moist - not light or airy.

The additional fat in the milk may through everything off balence, but I guess you can always try and see.