Honestly? Yep if I was in your situation I would have got rid of my agent and be dealing direct with DIAC and I would defo be emailing them but I would have also rang them.
I am a persistant and impatient one though but hey our application wouldn't be this far along so quickly if I wasn't!;)
Why would you not??? No offence but your agent doesnt exactly sound proactive (sure if it was his/her visa it would be a different story)- as has been said before those who chase things up do get the attention (perhaps unfairly?).
Go for it- you have nothing to loose and everything to gain:)