We have always found concierge to be worth the extra money. Usually the difference was around $60/night using discount codes. We may not consume enough to reach the break even point, but I think we get pretty darn close with breakfast, the bottles of water we take to the park, sodas, and snacks we eat throughout the day. The added benefit is the convenience of having the food and drinks available right there near you. It allows us to take shifts getting ready in the morning and we will meet in the lounge. It saves time and allows us to sleep a bit longer in the morning. Also, there is no fast breakfast option at the YC (this is my only complaint about the YC/BC). The pastries at the BW are a delicious option, however. Other bonuses are there will be no need to purchase refillable mugs and the concierge staff are great at getting you last minute reservations. Another factor may be the age of your children. Last summer we brought our 13 year old nephew as a companion for our 9 year old son. I thought our son ate plenty before experiencing the appetite of a 13 year old!
With regards to your specific questions - We were always able to fill up on breakfast. They have several juices, pastries, bagels, fresh fruit, and cereals. You may help yourself to as much as you can eat. Also, you can ask for as many water bottles as you like to take to the parks. It was also nice to stop at the lounge on our way back from the parks for our afternoon break and fill up on snacks and drinks. You can also take the food back to your room.
We've tried several resorts and our favorite is still the YC/BC. The atmosphere, location and pool can't be beat. Have a wonderful vacation!!!