The Enterprise D was destroyed so often during TNG's run, seven episodes by my count, and in two those it's destroyed multiple times (Cause and Effect, All Good Things). Also, the Galaxy class Yamato was destroyed in Contagion. Add to that, a few months prior to Generations being released we had also seen the Galaxy class Odyssey destroyed on DS9, and yeah, the actual destruction of the Enterprise D in Generations doesn't really have any impact. Don't get me wrong, the saucer crash sequence is a really well-done scene that still rivals effect sequences in movies of today, IMO, but seeing the Enterprise destroyed didn't really feel like the significant event it should have been.