Well IMO smart engineering normally suggests one concentrate on the "weakest" areas first that give the most bang for buck. "Worth" will be your own personal calculation. Not sure what your goals are other then "invisible", nor what else has been done or is in the planning to help decide if your cowl brace achieves much. Anything you add will likely show an increase in chassis stiffness, but is it smart or needed? Based only on what has been shared to this point, I'm skeptical.

Simplest trick to increase strength and remain the most invisible is to simply increase any member thickness, however the obvious weight penalty its not IMO the best bang for buck because if that.