1. Since I will use the camera not just for Astrophotography only, faster and accurate focusing is more important for me.
2. The 450D noise level is still unknown, but the 40D compares favourably overall.
3. The xxxD series are entry level while the xxD series are next level up. So it does not make sense to move from 300D to 450D.
4. The aluminium casing would come in handy during knocks!
However, the increased weight would put a strain on my imaging train, and it is also slightly more expensive ($1,850 for 40D compared to estimated $1,100 for the 450D).
Anyway, I still have the 300D and will send it to Hutech to convert it to a pure Astro camera.
Just my 2 cents.
