For me, the reason to get a 996 was to experience a completely different viewpoint of what Porsche thinks a sports car should be. The 996 interior is larger, the engine is more powerful, and the unique balance and handling create a driving experience that is nothing like the Boxster. They really are completely different cars. Its not about which one is "better" (as if that could ever be decided!).
I want to live and feel the full range of the Porsche driving experience. This is also why I also bought the 944 Turbo - another completely different view of what a Porsche sports car could/should be. The Boxster is incredible but its just a single iteration of the Porsche viewpoint. Porsche front engine vs mid-engine vs rear engine - I can walk out to my garage and experience the difference daily. When one of my friends wants to debate some aspect of these designs, we pull out the car and go drive it! Of course, next on my list is to own an old 911 so I can experience the Porsche air-cooled viewpoint and everything that goes along with it.
Additionally, we are living in an age where decent examples of various generations of Porsche sports cars are well within reasonable financial reach ($10K-$15K each). For the price of a new 981 (or BMW or Merc), you can own your own personal Porsche collection. I like to call it the "
High-Mileage DIY-Repaired Porsche Drivers Collection".
Last, there are some great deals on 996's out there (<$15K), you just have to look. Here is a link to my $10K 996:
http://986forum.com/forums/general-discussions/44227-986-wrecked-got-996-today.html