She was seducing Kashyk to save her crew. So she had her "well played" seduction powers at maximum level, hence the tension.
And yes I agree about the intellect, of course she had to tweak Sullivan. She may have found him attractive at first but eventually he would have said something quite parochial and it would have been a cold bucket on her ardor.
Janeway's personal log on Fair Haven:
"I met an interesting man there, and for a while I almost forgot he was a hologram. We weren't exactly compatible, but then again, Mister Paris didn't programme him to my specifications. "