I find the performance of Aperture 2.1.4 on my Mini 9 to be slightly better than it was on my 1.25GHZ G4 ALU PowerBook (although for photo editing the Mini 9 LCD is much worse than the PowerBook.)
I did have to hack the installation script to get it to install, however; basically you have to remove the "hardware compatibility" check.
Make a writeable disk image of the Aperture 2 installation CD, mount it and navigate to /Volumes/Aperture/Aperture.mpkg/Contents. Then edit the Aperture.dist installer script file to add a "return true;" statement as the first line of the function installationCheck() (around line 75.) Save the file and then run the installer - you should be good to go.