unless one is doing serious video or 3D the MacPros are total overkill.

Disagree on that one. My iMac 27" vid card suffers lag on generating previews when processing files.
It's something I have learned to live with... but it's a pain.
And I'm not even one of those guys with a really hi res camera like 30-60 MPs... I'm only talking 22 MPs here.
I am interested in another option though which is an iMac with TB and get an external card that is more powerful.