Am I right in guessing that the whole LS/DS thing only matters to Jedi and Sith? As far as I can tell, only lightsabers have alignment requirements and aside from crew affection, a few extra mail rewards here and there I haven't noticed any major impact on the non-force user classes.
In terms of gear I think it only matters to Jedi/Sith, but I've heard the storyline (or at least the side-quests) does change for the other classes depending on your side of the force. At the very least, the conversations will change, with some being more entertaining than others. I don't have direct experience of a non-force class yet.
Haven't played for roughly 4 months, so I don't know if things have changed, but used to be you had to be progressing in either light or dark while leveling to be able to keep upgrading your relics. All classes would benefit.
And it's not alignment that changes story outcomes, but specific choices. The game doesn't eliminate choice 'cause of a preference for light or dark; but a fork taken in the story does.