I am now deciding whether to get the 13" air or 13" MBP due to it's retina display which is amazingly sharp and clear. Don't really need the extra power, and its thicker, but may be worth it for the display alone. All the speculation sites say that it will be a while before the air gets retina and almost definitely not in the Next update in June '13.
Be a player. Splurge. Get the 13" MacBook Pro. Get extra RAM while you're at it. You won't notice the slight extra thickness once you're sitting and it's on your lap.
It's a pittance compared to your stereo equipment.