Some random thoughts...
It's hard to say just how much an effect Haruhi is having on the world based on her wishes. For example, she wants to meet aliens, espers, time travelers and see supernatural events etc. While some of those have happened, it's not been all according to the results Haruhi herself wants (so far in the anime and what I've read in the novel translations). ie, while she has technically met aliens etc, she doesn't know that she actually has. If Haruhi's wishes
created the aliens etc (something very hard), why can't her wishes result in Haruhi finding out they actually exist (which seems rather easy)? She does very specifically want to meet aliens or otherwise extrodinary people or beings. Based on that, it seems more plausible that the aliens etc pre-existed and are reacting to side-effects of Haruhi's powers, rather than being created by Haruhi.
Another example: Itsuki suggests that events 3 years ago created espers in the first place. However, given the specific conditions needed for his esper powers to noticible, it's just as possible that he always had those powers but it wasn't until certain events starting 3 years ago that it was possible to fulfill the conditions to realise those powers.
Another example: Haruhi clearly has some feelings for Kyon (she certainly doesn't like Kyon being paired with Mikuru or Yuki in ep 5), so you'd think she'd want Kyon to like her etc - but this doesn't seem to be happening at all. And if anything, her goddess powers are losing to Mikuru's moe~ power
None of which explains what Haruhi's powers are exactly or where they came from or the extent of the real results to date...