Part of the problem is the original design with the shock and spring mounted on top of the UCA. The other problem for you is a very heavy engine.
Even without spirited driving I think you may benefit from the extra bracing, not so much for corner carving, but just to prevent the towers from leaning in and flexing at the UCA pivot. Don't waste your time with the ones with a bend in the middle, they're just for looks as the bend acts like a spring. IMO, If you use the export brace you don't need the MC bar except for all out racing on slicks.
If you remove the force acting on the towers by placing the shock and spring on the LCA that would help quite a bit, but that may be more than you're willing to do to that car. Another thing to consider is what tires you're using. If you have relatively skinny P235-15 street tires, the tires will flex and the whole car will just slide and not transfer much of the load into the chassis at all if you're really generating a lot of force around a turn.
To illustrate my point, you can use any of the G-meter apps on your cell phone and you'll likely find that what you consider spirited driving on the street doesn't amount to much force at all.
You may not want to make many mods given its an R code, but anything you could do to lighten the engine weight would help.
Just my .02