I think if the writers had felt more confident in splitting up the crew it would have given us a better dynamic and more scope to introduce the next generation of characters. Chekov's role in STII gave him plenty of time to show his stuff and he did quite well in STIV too. Sulu and Rand's appearances in STVI were cool and it is a shame that it was decided that the Enterprise (Spock & McCoy) had to save the day instead of Sulu using the Excelsior's equipment for detecting gaseous anomalies established in the opening scene. Spock and McCoy saving the day looked cheesy and self-indulgent (they have 400+ crew including a number of scientists and weapons experts but McCoy helps Spock work on a torpedo...?). Uhura's big scene in STIII was more memorable that her enitre appearances in STII or STIV (the fan scene in Star Trek V is memorable to say the least - lol - and all joking aside, I thought it was nice to see Uhura get to do a bit more in STV).
I would have preferred it if they could have seen their way to work the supporting cast into the script in ways that allowed them to shine briefly rather than sit in the background for the whole movie. I really Loved Grace Lee Whitney's cameo in STIII and would have liked to see Chapel and Rand get some peripheral scenes where they could at least have been the focus of attention.
I think all the supporting cast felt peripheral to Picard and Data in the TNG movies but Riker, Crusher, and Troi felt a little more so. Troi did ok in Generations but I would have liked to see a bit more fire in Bev's belly in First Contact.