I recommend visiting DtD at least once during your vacation - great shopping (but if you don’t want to spend a lot on souvenirs, you might want to avoid it, as the Once Upon A Toy is very tempting for kiddos…).
It really depends on your ticket. If you have a ticket for the day that you can use, go into the parks for fireworks. But if you are ticketless, DtD is a great place to soak in the Disney magic without being in the parks.
Or… you could swim at the resort pool. Or visit the Boardwalk and watch Illuminations from afar.
Beware that parking and buses to/from DtD can be a disaster. We usually drive to DtD, but it’s very difficult to find a parking space. The buses, depending on where your resort is located, can take an awfully long time. It took us 45 minutes to get from the Boardwalk to DtD one night.
As for whether or not it’s worth it… all you have to lose is time. If you could be visiting the parks instead, I’d recommend that. But otherwise, DtD is a great choice.
*Oh, and be sure to make ADRs for a DtD restaurant if possible (I know Planet Hollywood and T-Rex take ADRs… that’s about all I’m sure of) - waits can be awful!