I think this was a scene very well achieved, it created a lot of tension. I think Mr. Archer was trying to be polite, while the Vulcan was rude in his one-word responses. Mr. Archer never meant to ask the question directly (are you spying on us?) until he was forced to do so by the rudeness of the Vulcan. During the entire scene I was under the impression that captain Vanik had a secret agenda. Why did he accept an invitation to dinner, only to later claim that he had already eaten? That's totally impolite.
I found Archer's politeness very forced and artificial, which seems to be justified with how quickly he boiled over. Then again, I never understood why the Vulcans in Enterprise when out of their way to piss people off for no reason. Surely humoring the "emotionally handicapped" species would be good diplomatically and oh... logical?
It is true that in the end the Vulcan has proved right, but I symphatised with the captain during the dinner scene. If someone invites me over to his / her place the least I can do is eat/drink what's offered to me, if for some reason I don't like it, then I at least I could pretend that I liked it, so as not to offend my host.
Plus, Vulcans of the 22nd century were probably being steered into the manipulation of other species for ulterior reasons.