Here is a quick 30 minute render. SL reached 10.29.
I hope you don't mind me posting my comments here, but I figure others can contribute based on what I saw.
1. You biggest killer is model orientation and design. Design can't be helped I guess, but by that I mean, there just aren't many openings for sunlight to get in this bad boy. In addition to that your model is oriented in such a way that the few openings that do exist (in this view) are not taken full advantage of. Perhaps you can use an emitter instead of the sun and place it where you want.
What I did:I moved the sun to 1300 in the middle of summer to try to get it high and get it in there. You had Sydney checked as your city, I used Madrid, and you had it set at noon. Noon isn't the best angle for your design. By the way, when I opened your model, "Physical Sky" was not checked.
2. Caustics. They were off when I opened the model.
What I did: I turned them on, but more importantly, I shut your glass off...it just wasn't doing anything for you. The abbe setting was on the default 63.5, but you should try higher settings like 150-200. Nevertheless, you need all the light you can get so I just hid the glass. By the way, your floor's material was set to glass. I don't know about that. I changed it to plastic with u and v settings changed to 0.3. I'm not sure on this, but I believe the caustics is still needed for the plastic and metal materials anyway.
3. Emitters. You had the normals reversed. Easy fix. In the rendering above I had the wattage at 150 each. You had 2050, so you can see what you'd get if you played with that.
4. I didn't have any of your textures so I couldn't do those.
5. Overall, play with your material settings. You had a bunch of stuff set to default diffuse settings, but I'm assuming this is a WIP.
Good luck and nice work!! I'll send you the file I've saved so far so you can check it out.
Later!
I'll be with you in a minute.
17" MacBook Pro, 2.4Ghz, 4GB Ram, GeForce 8600 256Mb