Well with your example with TNG, it's less feasible for them to have shown the damage because they only had the physical ship models to show in the space shots (a 4 foot and 6 foot model, if I'm right?), while Voyager was a CGI model, so you could always modify a copy of the computer model to show the damage. Also, the section cut out of the Ent-D wouldn't really have been visible on a 600metre, 42 deck ship.