Here is the thing. Its not a legacy thing as people have proven over and over again. The 1,1 has been crippled so that you need to upgrade to a new machine. Problem is that the 2006 MP is still a great machine. High quality sever chips and parts and ocotocore CPU power and up to date GPU. It cost me 6k to buy my MP and I am not going to spend 20k to get a new one when the old one works fine just so I can airplay. I am not alone on this. I have bought my wife a galaxy pad and am ready to make the change. I know when I am being taken for a ride and denying a patch for the 1,1 is a scam.
1.) Where is the crippling. There are Macs with EFI64 that aren't going to get ML support either. Mini 2008, Macbook 2007 have EFi64 yet don't get ML support. It is not just an EFI64 and the ability to boot a 64bit Kernel that means you get an ML upgrade/
2.) Definitely don't spend 20K to buy a Mac Pro to Airplay, as you will be even more disappointed when you find out that AirPlay is only supported with Sandybridge and Ivybridge based machines. You won't find a Mac Pro listed.
http://www.apple.com/uk/osx/specs/
AirPlay Mirroring
Requires a second-generation Apple TV or later. Supports the following Mac models:
iMac (Mid 2011 or newer)
Mac mini (Mid 2011 or newer)
MacBook Air (Mid 2011 or newer)
MacBook Pro (Early 2011 or newer)