Guess we're not quite done yet - LOL. Just another point of view from our experience, but let me start by saying we never buy the drink packages. We are D+ so we each get 5 vouchers. They are combinable in that I can use hers for me and visa versa, so for us the 10 combined daily pretty much covers our requirements. Especially when you factor in port of call days. We also typically only use them on alcoholic beverages, and with the voucher value at $15 we have never been denied a drink of choice. Water (above that provided) and soda, etc., would be a la carte for us.
So on the occasion where our vouchers have been used and we would want additional drinks of any type, paying for them a la carte would never reach the cost of the beverage package. On port of call days when we may have unused vouchers, we cash them in prior to going to bed for unopened canned and bottled beverages (beer, Truly, soda, water) and take them back to our stateroom for another time. It has always worked out well for us.
With 8 combined, your results may vary. But do the (rough) math - the approximate breakeven for the packages is about 6-7 drinks per day per person, including port of call days. So with your 4 vouchers each you would need a total of about 10-11 drinks per day per person every day to justify the cost, since you both need to buy it. Again I'm focusing on only on alcoholic beverages. Maybe it will work for you as it does for us. Just saying....