I think not keeping Decker, Ilia, Saavik, and David Marcus around longer was a missed opportunity.
This! Although it was hard enough to get enough screen time for the classic characters from the series, adding in more regulars would have really condemned them to the back.
A shame, really, since they were all created as very dimensional, intriguing characters.
I agree. In fact, I 'resurrected' Decker, Ilia, and everybody on the Epsilon IX station for my online comic. I decided it might be fun to explore what that might mean for them personally, how they might be viewed by other crewmen, and how non-Federation races might view them as near-mythical beings who had been beyond the mortal world and returned as prophets, seers, angels etc. Plus it allows me to explore themes about their 'humanity' are they really Decker and Ilia or just biological probes sent back by V'ger? Were they sent back for a particular reason? And so forth. Ieven did the maths and, assuming that Saavik was the same age as Kirstie Alley in TWoK, she could just about be a midshipman or ensign around the time of the second 5-year mission so maybe I'll go the whole hog and feature her too.