flexy frame fix, more k-force?
 

Rider weight and bike model aside, would an external bottom bracket help aleviate the effects of a flexy aluminum frame or amplify it?

Rider weight and bike model included, I weigh 150 and have a vitus 979. Thinking about a modern campy groupset and wondering if standard square taper BB would be advantageous over the UltraTorque crankset.

Makes no difference. The interface (BB) is the same, whether internal of external bearings. The Vitus 979 is flexy, period. You must learn to ride it....more spinning. If you're a gear masher, your heart to skip a beat when that frameset flexes. :)