Pick up an un-welded, no reinforcement k frame to about 3 feet and drop it flat to the pavement and listen to the noise it makes. Then box/weld it and do the same test. Big difference in the sound. I think that means something...

I am glad you guys want to science the k frames but I can tell you already - real world testing proves beyond any doubt that it's necessary and makes a big difference in a cars handling.

And as to adding more spot welds vs a full weld - the full weld wins every time. Break out the mig welder, weld everything.