As I brought up last summer (Tasks for Automation) the intent is certainly to have a set of scriptable commands.
Basically, you want something like:
from avogadro import sendMessage
for filename in glob.glob(*.xyz):
path = cwd + "/" + filename
sendMessage("openFile", path)
sendMessage("selectElement", 1)
sendMessage("showSelectedAtoms", False)
sendMessage("saveGraphic", path[:-4] + ".png")
And yes, your point would be to select for example based on a SMARTS pattern.