We just got home yesterday from the POLY GVC with dining plan...sniff sniff!!
It was so great to have BOTH. I will just say that this is how we seem to operate but it is just our family and our opinion!!
We would have a quick bite at the concierge lounge for breakfast between 7:30-8:00am. It was fine to have a cup of coffee, bagel, croissant, fruit--melon and grapes, danish. My kids drank hot chocolate/milk with cereal and a banana. But honestly- after 6 mornings of the same stuff we were getting a little sick of it.
My kids were always hungry again by about 10-11am...me too

and it was great to use a couple of CS coupons to have a snack. We used a couple of TS coupons for lunch one day but the rest of our lunches were CS.
We were always back at our resort for a swim/nap and a few cookies/soda and gummy worms between 2-4pm. BUT we were always heading back out to a different park between 4:30-5pm for the evening. Therefore, we never were at the concierge lounge between 5-7 when they served appetizers. (We did hear one family telling their kids they had to wait to eat until 5pm when the food came out and then to eat a lot because there would be no more food for the whole evening

)
Only 2 nights did we make it back to have a dessert or a glass of wine before 10pm.
We loved the concierge lounge and would definitely go concierge again. But it was not for the food offerings and we loved the dining plan because we could eat at lots of different places that we normally wouldn't eat. We used our snack credits for water bottles/popcorn/Mickey bars. Our TS credits were used at Chef Mickey, CRT, Ohana, Boma, LeCellier, Sci-Fi.....It was fantastic and I see no reason why staying concierge would exclude the dining plan. They are both great!!!!!