Well, I usually think of the lined graph as impying a continuity between the points; I want to state that it happened at a specific time, with nothing in between. I also kinda like the bars in that is draws attention to them; the dots are to easy to overlook (especially the color, to my eyes).
So, I've taken some of these ideas and gotten the timing down better, and applied alpha so that I can see overlapping bars. This might be good enough for now, at least for me.