I have been itching to test drive a BRZ just out of curiosity. The same comparison has been going on for years. Back to the 944/RX7 days. The Porsche has always lost the "value" category. However you do get the benefit of better materials and feel.
Some people only want to buy new cars with factory warranties. That makes the Boxster out of the price range for many people.
However for me I can say for sure that pulling up to the Opera house after the nutcracker to pick up my girlfriend in front of 100's of people felt much better in the Porsche than it would have been in a subaru or scion.
Conversely I get much more worried when parking in hobo territory overnight.