I would change the title or at least the headline in your first post to say this mod will work with the 2011/2012 WRX (just to clear up any possible confusion). Other than that, I like the new flow of the DIY. Everything makes sense and the pictures looks good.
And on that note, here is my completed key:
Shell: $25 (xluben)
Legacy Donor Key: $30 (eBay)
Laser Cut Blade: $40 (local locksmith)
Total Cost: $95
Overall I'm incredibly pleased with this mod. Even though I had to hack up my valet key to get to the transponder, I'm perfectly fine with it since I now have 3 working master keys. Also, I highly recommend shopping around for a local locksmith to cut the flip key blade. I didn't trust myself with a dremel and a cutoff wheel enough to mess with modifying one of my keys and the $40 price to have the key cut was totally worth it.
Thanks for the great write up!