You don't need a monster machine for general graphic design.
I'm using mostly indesign day in and day out, with a bit of Photoshop and Illy thrown in - sometimes Flash all using CS5.5
I don't even use a Mac 
Operating System: Windows XP Professional (5.1, Build 2600) Service Pack 3 (2600.xpsp_sp3_gdr.130307-0422)
Processor: Intel(R) Core(TM)2 CPU 640 @ 2.13GHz (2 CPUs)
Memory: 3070MB RAM
Unless you're doing large amounts of photoshop then I guess a SSD would help to load and save very large files faster.
I always say 4gb is plenty for RAM
8gb is plenty for photos
16gb for extremely large photo/video/animation
You need processing power well if you're doing a lot of processing! Like video editing or animations - but for general day to day InDesign work having a massive engine in the car won't get you there any faster.