As demonstrated by the lady in the park. She certainly made Watanuki happy, but was totally harmful for him. My theory is that she was a "Nothing Woman", which is a manifestation made by the spirits of women who lost their children to war, famine or illness... or at least, that's according to Inuyasha.

Yeah, I've read it, and it's definitely too cute for words. :3
Though I was terrified for a moment that her food was noxious, or something, and Doumeki would suffer some serious consequences for eating that morsel of her food.

You haven't lost much. The second season deviates too much from the most important aspects of the plot, but it does have its great moments. The birth of Tampopo, and a moment in the last episode when Watanuki actually grabs Doumeki and claps his hand over his mouth (and nose) to stop him from saying I-don't-remember-what, and Doumeki actually begins to turn purple... then blue... but doesn't struggle to free himself at all. Methinks he was just too happy to have Watanuki grabbing him. XD
I was actually considering turning that little bit into an icon with "I can die happy now" over him. XD

Watanuki can't be the only one Yuuko flirts with. I think that's just one more way in which she projects a threatening image. It certainly would help to reduce any male customer (which we've never seen so far, save for the old man with the moon birds) to a drooling and nearly incoherent (and totally manipulable) mass.
I still think (in typical fangirl fashion) that all her teasing about love is actually directed towards Doumeki and him. Hey, I can dream, can't I? :P