To what extent does the location of a conference impact the number of submissions? Some conferences take place in locations that are considered to be more attractive than others to most people (e.g. UIST 2014 @ Hawaii). Some can be more easily accessible than others. Etc.

Is there any research/study/survey that looked at the impact of the location of a conference with regard to the number of paper/poster/etc. submissions?
I don't know of a specific study on this matter, but I can at least offer one piece of data.  There is a conference that I frequently attend which has a community mainly composed of Europeans and Americans.  As such, it switches back and forth between the two continents each years.  The American contingent is smaller than the European, however, and there has been a clear pattern of American years having lower attendance than European years.  This has been attributed, on the basis of a lot of anecdotes, both to the difference in travel expenses and also to restrictions on the use of travel funds by some agencies on each side of the Atlantic.