Can I substitute a TS for a QS meal? I understand why you wouldn't be able to use a QS for a TS credit, but since it would a cheaper substitution I wasn't sure if this would be considered ok?
yes its quite common to have ts left on meal plan and they will let you use it for a cs meal instead.
Yes, but if you're planning on doing that, you probably shouldn't be getting the dining plan in the first place. You're effectively spending about $40 for a $12 meal.
Unless you have the ability to plan out all of your meals and stick to that plan, so you don't have any "extras" left at the end of your trip, the DDP is doing nothing but wasting your money.