A target is better than the end my ship met- at the end of a scrapper's torch.
A few of the ship museums do try to exercise some of the equipment. While none of them light off boilers or cycle the main propulsion engines (except the Merchant Marine ship museums like the SS Jeremiah O'Brien or the SS John W Brown, who actually go and cruise), several have reactivated the emergency diesels. Some of the Sub museums keep the main engines in running condition (or some of them, with parts of the non-ops used as spares). Most of the others, the Navy scavenged too many pieces for the equipment ever to be brought back online, and any spares or the parts that could be used to complete the cannibalized equipment went to the scrapper years ago.
It'd be extremely satisfying to see some of the old great WWII museum ships steam under their own power again, but aside from the logistics of making it possible, I doubt the State Department would allow it to happen.