That depends if it needs service or repair. In the case of repair, sadly, it’s often not worth it.
You see, dual or double cassette machines were some of the cheapest cassette machines of their time. Now, consider that cassette deck maintenance can be some of the most intensive and therefore labour intensive work we do.
How many cassette deck mechanisms are in a double cassette deck…? Two! This means doubling the already time-consuming technical workload in most cases, and that can mean quite a few hours of work in total.
If both decks work and they need cleaning and service work, then yes, it’s probably worth doing. If the deck/s need repair though in the form of idlers, belts etc, then no.
Is it worth spending much time and money on a deck that might be worth $100? This is a question for owners of course and there are more than just financial considerations, but the low inherent value of this sort of cassette deck makes all but standard service work often not viable.