Yeah, I like how they worked her problems into a drug habit rather than a pregnancy, which I was dreading a story line about but almost expecting.
I don't see hers as a human problem when you consider that Vulcans, from a historical standpoint, were a very aggresive and irrational species before they embraced their beloved logic as a way of life. I see her drug habit as an interesting exploration of the Vulcan species, showing that they aren't always as "in control" as you might think.
On the matter of character flaws, one of my favorite species that hit the Star Trek universe was the Cardassians. DS9 providedthe perfect opportunity to get to know them better, but never exploredthem as much as I though they should. In the Cardassians, we had a people that had at one point been very peaceful and spiritual in their history, but desperate situations (plagues, minimal natural resources in their home solar system...) led to desperate measures, military overthrow of the civilian government, draconian laws to control rampant crime, and of course the occupation of Bajor.
Here you've got a group of people, some desperate to hag onto the power they have build in spite of the ugly way they have done it and others just as desperate to prove that Cardassians are not the blood thirsty butchers so many have come to think they are.
Lots of potential to explore an interesting species that I felt went sadly under explored.