I'm wondering if i may be doing something wrong.
Some of my renders can take from 8 to 12 hours to render (& sometimes more). I use a PowerMac G4, Bryce 4 and i render at Normal quality anti aliasing with spacial optimisation high and the size is usually super 8mm (although i would probably like to make it larger for printing).
I don't feel that my compositions are that complex as i rarely use lights or smoke etc.. & after just a few boolean ops it really slows down. I do however like to use some mesh objects imported from Amorphium.
Does anyone have any tips or know of a tutorial that might help & would getting more memory 'significantly' improve the situation?

more ram will speed up osX. make sure you have fle sharing OFF disable clock turn off monitor I have renders that go for over 24 hrs sometimes....

I'm sure you've looked at your mats. If you overlap transparencies, or worse yet, overlap volumetrics, expect the render engine to grind to a crawl when it traces through those areas. I once had a stained glass image go from about a 5 minute render to an aborted all nighter just because two of the glass textures overlapped when I moved the camera.