Is there any evidence that graphical abstracts are beneficial? I've seen some journals now require (or at least suggest) including a graphical abstract for publication. In particular, Elsevier/Cell seems to advocate strongly for graphical abstracts as they can draw attention and attract readers. 

There seems to be anecdotal evidence that this is the case. But, is there any study that supports this assumption? Does a graphical abstract lead to more readers, more citations, more media exposure, or improvement in any other metric of "impact"?

The only study I've found that tackles this question actually finds no evidence of this being the case when analysing papers published between 2014-2015 in the journal Molecules.
I'll note that you aren't going to get citations just because your abstract is "interesting". Especially if it is just interesting "visually". Your work has to contribute to a thread of research that someone else wants to extend. A casual reader might say "cool", but that won't result in a citation. 

But you need interested readers who are working in your field and whose work will benefit from your own. You need to reach them, of course, but the venue in which you publish would, it seems to me, be far more important than any "flash" in an abstract. 

No, I don't have any research, but would doubt much if any effect. Spend your effort where it does the most good. 

Places like Nature get a lot of sophisticated but relatively casual readers who just want to be kept up to date. A visual abstract will help them. But they aren't the ones doing the work that will cite your work. 

So, yes, beneficial to the casual reader, but not necessarily a citation builder for yourself.