I'm not an engineer but that brace looks like useless redundancy to the lateral portion of the OE subframe right in front of the cat brackets. The lateral braces I see most use in the center of the chassis are rearward of the cats where there's zero OE reinforcement.
Additionally, I checked out the "suspension member stay" on my Z and would be hesitant to remove those as they appear to be providing rigidity to the unibody. FWIW, the aforementioned aftermarket lateral braces typically have extensions beyond the frame rails to the unibody just like Nissan does with the suspension member stay.
Check out the 4th pic in this link of a more substantial brace in the same position that retains the suspension member stay feature via the brace itself. They have other options for that areas as well but all appear to retain the suspension member stays in one form or another.
https://www.soulfunction.com/product...nt=37390503118