Eh, well, Haruhi didn't give me the impression of someone who is as calculating when she wants something. She reminds me of a girl I'm playing with sometimes. She's always hyper, and when she wants something, she just states so and takes it. Like how Haruhi acts with everyone in her club, especially Mikuru
The same is apparent when Kyon talks with Yuki and Itsuki about Haruhi. The theory is that if Haruhi gets bored, monsters and all sorts of calamities appear, so we have to keep Haruhi pleased. This adds to my impression that Haruhi really doesn't hold back when she wants something. What seems to be the case however is that she doesn't actually WISH for something to happen if she feels the current situation can be handled as it is or is interesting enough to keep her occupied. Which means that if at some point, Haruhi gets frustrated because Kyon doesn't reciprocate her feelings, she'll probably wish for something drastic.