Protein powder is nt a magic bullet, it just helps you get your requirements met if you are deficient (which by the way, most Americans are NOT).
Evidence for which can be seen at the local mall's food court.
I'd offer one modification to this, and that is on off days get whole food. Protein shakes are absorbed very fast and are more suited for use around workouts where quick bioavailability of protein and carbs is needed. From a nutrition and cost effectiveness standpoint it's best to use them on workout days, pre, post or both.
During off days you really should have a good, constant stream of nutrients and whole food is the best option. For protein, beef jerkey or canned/bagged tuna, and for carbs, raw oatmeal and flax meal are good options for portable food sources. I always have a few cans of tuna in my desk at work. Take it easy on the flax though. That much fiber and protein in your diet is sure to liven up your digestive system if you're not used to it.
If you want to use a shake to help fill out a caloric defecit and turn it into a surplus, don't use the shake to replace a meal, use to augment one.