If you are on the QS plan you will not have any credits useful for TS meals. For an adult its $10 more for the Basic plan where you'd have a TS credit available everyday.
Let's say you're staying 5 nights, it would cost $50 more to upgrade each adult to the Basic plan. If you are going to spend less than $50 OOP for TS meals I'd say keep the QS plan if it suits your dining style. However, if you're going to spend more than that and wouldn't mind a daily or almost daily TS meal I'd say go for the Basic plan. You will need to make reservations and pay tips at those TS meal, but if you'd prefer the TS meal anyway its a good trade off in my book.
CS credits are for QS meals and TS credits are for TS meals. You can't trade either way. (on occassion you might be able to trade TS for CS, but that's not a policy and not usually a great value).