Well there are two aspects to your question. First financial:
2yo eats for free and the 4yo will eat for $10.99/day, a steal if you ask me. Since you plan to do some TS character meals I say go for it as for $38.99 you will get those meals plus a CS meal and snack each day.
Secondly, now how to select those character and other meals:
I actually think breakfast or lunch character meals will work best for your little ones. They'll be awake and not cranky or too tired. Generally I suspect you'll have less wait to be seated time even with ADRs. Lunch might be the respite you need from the hot parks and it'll give you a chance to refuel. I think lunches can be scheduled from about 11am to as late as 3pm. A CS dinner at your resort will also be a sit down meal and you can even do this in the comfort of your room or patio area to make it even lower stress. If you plan to go back for naps/rest this will also eliminate any mad rush to get them up and running again in time for an ADR. I remember reading a post where one parent stayed with the kids, the other went and enjoyed a solo CS meal, brought back food for the family. I can't recall if the other parent went and had their alone time meal, but that is certainly and option too.
Sounds like you'll have a magical trip whatever decisions you make. Be sure to capture those precious moments on film!