I had the same problem not being able to save template files and the information above was really helpful - thanks guys - BUT it didn't completely solve the issue in my case, because, it seems, I have two drives on my Mac. I offer my solution in the hope it might help others with a two-drive system (and reduce the amount of time spent lying down in a darkened room).
I run two drives in my Mac mini - the system drive (SSD) and a a bigger (1Tb) conventional hard drive where I store my iTunes files and folders and my Logic projects, as well as photographs videos etc.
My username 'Home' folder on the system drive has the usual Music folder but it is in fact an alias pointing to the actual Music folder on the HD. iTunes has no problem with this alias arrangement - I have used it for more than three years. But Logic X does have a problem. My solution was to make my username Music folder on the system drive a real folder (not an alias) and create the subfolders suggested above (music/audio Music Apps/Project Templates) and it worked - I can now save template files. I don't understand why Logic couldn't follow an alias - like iTunes can - but at least I found a solution. (iTunes is still operating through an alias which directs it to the HD).
Anyway I thought I'd share this - in case anyone else with a two drive setup is going nuts because saving templates doesn't work like it should.
Paul