At first reading this I thought it was nuts... would be talking $30 more per day, per child to do this.
BUT.... with free QS upgraded to regular dining you're talking $10 per kid each... so $20 a day to upgrade both of your kids to regular as "adults'. If kept them as kids, it would be $2 each, so $4 per day.
You're talking $16 per day to upgrade both of them, total.... yes, I think it is worth it. I think that $214 number you mentioned is correct what it would be.
If doing buffets, won't matter, as kids or adults, have same access to amount of food. For counter service/food court I don't think you'll find much more variety or food or advantage to making them adults.
Other table service meals... yes, can be worth it as long as they like what's on the adult menu. Do they usually eat off the adult menu when eating out at home locally with you and have the appetite to do so? If so, then yeah, could be worth making them 'adults'. If doing a lot of table service at nonbuffet restaurants, I think yes, could give them a lot more variety - if they want the variety. I have one kid who if every restaurant had a hotdog on the menu, he's thrilled and that's what he wants! Also, if adult meals too big for them and can't finish.... then you can if still hungry! I know for CRT I LOVE the Major Domo's pie and can't wait till my now "adult" daughter orders it and can't finish it all - more for ME
My daughter that becomes an "adult" this upcoming trip is so excited to eat off the adult menu, but in reality I know that many times she will end up not liking what's on the menu, and want off the kids' menu - which hopefully they'll maybe give her a bigger kids portion?
Take a look at the menus where you'll be dining... see what variety there is for the kids at those places, and what off the adult menu they may like to help decide.