Years ago, a TS Dining Plan did save you money I remember. Now, it's more or less break even or even pay more.
However, to some people the convenience of having everything paid for (minus liquor and tips) is worth it.
I'm going in 3 weeks and opted for the Counter Service plan. I'm going solo and don't want to worry about hopping around DIS to meet my reservations. If I was going with family, I'd definitely opt in for the table service and not worry about prices or anything.
On the TS plan, I always order the most expensive thing typically to make it worth it, (ie crab legs, steak, etc...) to recoup the costs.