Why? You own a great laptop. I'm sure it has more than enough horsepower to meet your needs. I use some fairly CPU/GPU intensive applications and I can tell you I don't feel the need to upgrade my 2009 MacBook Pro with its ageing 2.8 Ghz Core2Duo processor.
I did do a clean install on my MPB laptop recently though. I'm not sure if Apple computers are supposed to suffer from the same bitrot that destroys Windows installs over time. But I was encountering a lot of beachballs and generally sluggish performance especially 5-10 mins into a reboot or wake from sleep. I tried all the usual fixes. Disk Utility, Fix Permissions, Reset PRAM, cleaning caches etc. Nothing worked until I did a clean reinstall. Now the machine is running like a dream again.
These new MBPs to look nice. But I don't need one. And I won't be rushing to blow thousands on a new laptop when my existing model is more than adequate for my needs. I used to buy a new Windows laptop every 18 months. I definitely no longer feel the need since I started using OSX as my primary operating system. And that's a good thing as far as I'm concerned.