I'll agree to a point that I thought that the perimeter spotwelds appear top be adequate. Often times I defer to those that seem to have more experience, then occasionally second, and THIRD guess the decision.
One thing that makes total sense and I can't WAIT to prove it to my self is the benefit of the STEERING BOX MOUNT GUSSETS. I wrote in all caps to make sure it wasn't missed.
If Firm Feel thinks that it is important, I'd tend to follow their suggestion. It was an easy decision for me because I had a spare K member for my car. Its far easier to work on these things on a TABLE than under the car with the engine still in there. For me, I just looked over the steering box area and filled in all gaps with .125 wall steel plate. Pretty simple really. I also made sure to NOT encroach on any area that could interfere with the mounting of the steering chuck itself. I test fitted a PS chuck to be certain. Then I welded washers around the LCA pivot holes. I have personally seen these ripped out on cars that ran too long on bad LCA bushings or others that were involved in a collision. Imagine what them Duke boys did when they jumped the river at Seminole Canyon! Finally I added similar washers over the strut rod hole. This area I also have seen pushed in from collision damage.
All in all the modifications that I did cost me about $10 plus whever Argon and MIG wire I used. Oh yeah... the 220V electricity, the sawzall blades to cut materials and the grinder discs to hide my"less than stellar" welds. Lets call it $20.
My opinion of this mod? It MAY provide more precise steering response since I am running some pretty wide tires. Less deflection when I encounter a bump with one wheel too. The washers welded on? If it saves me from a damaged K member, thats great. All the perimeter welds may have been for nothing, but the other areas should provide some benefits. Opinions may vary, of that I'm certain.

Oh, I forgot to touch on this point:
Drag racers that do not complain about handling deficiencies? I would think that the straight line guys would be more concerned with how well the cars track at 120 mph on a smooth surface rather than take their cars on bumpy, twisty roads with 195-75-15 front drag tires. The skinny tires give up traction before the flimsy steering mounts see much stress. They may have never noticed any K member flex at all.