Last I checked, Dining with an Imagineer at Brown Derby was available only three times a week (MWF), and had total space for no more than around eight to ten guests each of those three days. The only way I was able to get it was to book it towards the end of my stay, using the 180+10. As it turned out, the imagineer I got was not in the field I'd hoped for, nor as knowledgeable of Disney history as I'd hoped for, and my food order turned out wrong. If I had it to do over, I'd skip the whole thing, although I think with a different imagineer, I might have liked it.
(I have no experience with booking the Cake Class.)