For all the armchair engineers in this thread I have actually just fitted a Weichers strut brace and it is definitely not just cosmetic. There is a clear improvement in turn in, less understeer and less steering deflection over bumps. The coupe is a stiff body but the front chassis legs are long and the standard bracing to the firewall doesn't work in the right dimension. I am certain I can feel a lot less flex and the suspension is picking up more of the task of absorbing bumps. Yes you can flex the bar slightly by leaning on it but that's not how it's loaded in practice. Could it be stronger? Yes. Does it need to be? I don't think so based on actual results after fitting.
For all you N52 owners I can recommend the Weichers brace, I liaised with them and they told me I needed the 3.2 version in aluminium rather than the steel one. It fits perfectly, clearing the air intake and the engine plus oil filler cap. You can get the same shape in carbon too but it's nearly twice the price.