I wouldn't skimp on the ADRs. Very few walkins these days regardless of how you are paying.
That's always assuming they want to eat a lot of TS meals. Don't forget you can book last minute ADR's - I've found that you can usually find something decent just a few days out. I had booked a solo trip for early December 2010 (Pop Warner week) with no ADR's and then ended up taking family along and booking ADR's a week out. I got everything I wanted - Le Cellier included. When you don't have the dining plan, there's not so much pressure to make ADR's - you try, and if you don't get something, you just move on to plan B.
Going without the dining plan gives you the freedom to be more spontaneous, and that typically means more CS dining because you're only eating when you're actually hungry, instead of eating because the clock says it's time to. There are a lot more CS options than there used to be, so it's not all burgers and fries. I can be there more than a week and not have the same CS meal twice, due to the wider variety of options.
If they go TS, they will have the freedom to split meals any way they like. They can go in and just order appetizers for a light meal (which I have been known to do and which aren't on the DP any longer). I like an app/dessert meal, because if I eat an entree, I never have room for dessert.
I'm checking in for 10 days on Tuesday, and have one ADR booked. I'll either eat in my villa or I'll eat CS the rest of the time. I've never used the dining plan because I don't spend as much on food as the plan costs, and as a solo traveler, a good discount code typically beats
free dining hands down. I prefer the spontaneity of just stopping for a quick bite when I'm actually hungry instead of planning my day around having to be at a certain place at a certain time, and I don't feel the pressure of "use it or lose it".