I really do think it depends on the character and plot. Daniel/Sha're made sense and that was canon. It added to the characters. And like you said, same for Sam/Jess. As much as I dislike it most of the time, Clark/Lana is essential in building Clark's teen years.

Sometimes writing takes missteps and sacrificing character or plot to push the romance. I see that having happened in several shows I've watched.

I think if more shows would just let the character fall naturally into place, then if there was any ship, it would follow.