We've saved big $ with ours, as we do a lot of signature dining with wine. it also includes valet parking at the resorts (saved $40 right there on our last trip).
With you meeting another family, your group could easily spend $300 in just a couple character meals or nice dinners; so just take a look at all your TS ADRs, make sure they're covered by the DDE. If you are doing 2 TS meals a day, times 5 days, times say 6 people... you probably will save $. NOTE: while it does include parties of up to 10 people (all ages) IIRC the bill must be one check (they won't divide the discount) so make sure everyone knows that (bring cash/rotate who charges, etc.).
Forgot to mention that the DDE now includes an 18% tip on all checks; (we always tip that or more anyway, just wanted to mention it). FWIW.