Yeah, those ladder braces help, and I agree about the cheap chassis stiffening when you have scrap metal and a welder

Those ladder braces would help, but the most noticable improvements for chassis rigidity are the ones that increase the torsional rigidity of the car. Torsional rigidity is really the standard measurement for analyzing frame stiffness, and the only area that makes a difference is the area between the front and rear strut towers; all front and rear overhangs are inconsequential. The most effective stiffening modifications are the ones that will prevent twisting force between the towers. Fender bracing will help tie the strit towers to the firewall a bit, but you still have the problem of the front bulkhead (firewall) twisting in relation to the rear bulkhead.

Cages help tie up front and rear bulkheads like whoa, and so does seam welding.