First, consider the simple thought experiment that if a) people tend to cite work they've seen/heard about and b) people pay attention during conference presentations then it follows that there must be some positive effect of presenting at conferences. Of course, this isn't very helpful to answering your question.
I don't think that it is possible to answer this with statistics or evidence, because any sort of study would only be able to show correlation between presentations and citations. And surely there is some sort of correlation: consider that prominent researchers often attend conferences because they may win awards from the conference, they are more likely to give keynote presentations, or they may be involved in the organizing/steering committees.
The actual direct effect of gaining a citation because of a presentation you gave must be extremely small. Consider that in the audience you present to, probably only a small amount are directly working on the same problem as you. And if they're already working on the same problem, they're most likely going to cite you anyway, regardless of whether they hear your talk or not.
Last, I'll offer my personal opinion that the benefit from giving a presentation is not that it increases your citations, but rather that it offers a networking opportunity. If you give a memorable talk, especially one that people in different subfields find interesting, they will remember your name and your work, even if they don't cite you.