With the limited upgrade ability of the new Macmini, I also would recommend jumping up to the G5. Of all the things I do on my Macs rendering is the most demanding. Look at a G5 iMac with 2GB, if you can't spring for a TowerOfPower. Don't worry, I'm still going to buy a Macmini but not for rendering;-) To answer your question, yes you will notice an improvement, but this is a how long is a piece of string question. We can't quantify your improvement.