I didn't like how dogmatic she got in season 6, but of course Willow didn't debate her at all (and a philosophical and theological debate should've been as stimulating as a historical debate she had with Buffy in season 4), she just expected to be obeyed so Willow annoyed me a lot more than Tara. It's too bad that the writers couldn't have Tara explain her reasons more as it could've been interesting (and also come off as less dogmatic), though sometimes Willow was just being downright silly in her recklessness when she had simpler ways--magickal ones at that--which would be even more effective, and Tara could've suggested things, like that light to find people Willow could easily cast rather than shifting people into another dimension for a second. But the writers were being especially heavy handed with the characters in season 6 to make the story go the direction they wanted.
And I realize Tara spoke more from the heart than the head, so I try not to hold it against her that she comes off as dogmatic rather than rational or clear headed because I know some people have a very good intuitive grasp of the situation (artists and those who must navigate abusive families or survival situations often have this way of thinking, and not only does Tara fit into that, but she's also an empathic witch able to read people at a supernatural level, so it strikes me as likely that this is true for her) but find it hard to verbalize. I have a close friend like that and I enjoy helping her find a way to verbalize what she feels, but of course Willow just expects a clear verbal explanation right away, and given how she was portrayed in season 6, Willow might've actually gotten a lot more angry if Tara had (which of course Tara would sense).
I personally didn't find her boring, though did seem more Willow's sidekick (and later Buffy's counselor) rather than a true Scooby, and I think they should've had more Tara-specific episodes (offhand, I only recall the one where her family comes when the rest are actually more Tillow centric rather than Tara). Sometimes big insecurity can alienate me, but that's the very clingy and/or paranoid (where they constantly sense insults, rejection, etc, where none is intended, and thus demand constant reassurance which I find tiresome), but Tara's insecurities didn't manifest in those specific ways so it didn't bother me.
