Things that you do want to kind of splurge on a little bit in a Motion Graphics focused workstation is RAM. A lot of programs you can get away with 16-32 gigs of RAM in most systems these days for fairly high end stuff.
But when you got Motion Graphics, it's not crazy to say, minimum 64 and up into 128 gigs of RAM or higher in some systems if you can afford it. It really does help because so much stuff is cached in memory.
When you're doing these Motion Graphics previews and stuff. It really helps get real-time playback or close to real-time playback. So you can kind of zero in on what you're doing, especially with larger compositions.
For more info on motion graphics check out this great guide on the principles of motion graphics: