If you ditch your PPC Macs totally, you won't have any themes sans Iridium/Uno. The only way to theme an Intel mac is by replacing elements manually. Much like Themechanger but not automatically. The only way to make an Intel compatible Extras2.rsrc file is by using Extras2Extras2 by Colin Cornaby
Direct LInk. I'll give you and example of a possible scenario.
Go to (on a PPC) ~users/library/caches/shapeshifter/*long ass name*/Theme and grab the extras.rsrc, finder.rsrc and the spotlight search files.
Take that file over to the Intel mac and run it through Extras2Extras2 to get an Intel Extras2.rsrc file and save that and the other PPC files to a folder somewhere.
Go to system/library/coreservices and replace the finder.rsrc with the modded one (back up the original).
Go to system/library/frameworks/carbonframework/frameworks/HiToolbox.framework/resources and replace the Extras and Extras2 files with the modded one (back up the originals).
The spotlight file names will have to be adjusted to match what's in the system/coreservices/search.bundle and then replace them (back up the originals).
You'll have to do this similarly for all of the app skins you want changed. (ugh)
*Taking a themepark file and exporting the theme to .dtla to get the themed extras rsrc file has not worked for me*
*Currently, Extras2Extras2 only converts PXM files, no PPATs yet and that means no text color changes.*
It's quite the pain in the arse.....