I have a 2010, stock arb is 21mm front and if I remember right 16mm on the back.
I bought the car with 51k miles on it and after a couple thousand miles I noticed a slight knock and a bit of wiggle under hard braking, inspection showed the rear bushing on the front control arms was perished so decided to change out both bushings on the front wishbones.
I don't notice much more noise over all other than some hard bumps can be loud, handling wise it improved by feeling more solid in the corners and easier to maintain going straight, overall less floaty, this car does feel a bit numb stock.
The rear subframe lockdown kit I would say makes one of the best changes, again it helps the car feel more solid and less floaty. Overall more stable when cornering with a bit of speed.
I did try it on lowering springs which was great around town and for roundabouts and cured the understeer but I scraped on every other bump and once you get above 80mph it felt like it jumped over sharp bumps rather than absorb them which left it feeling a bit sketchy. So I'm back on stock springs, after looking into coilovers it's just not viable for my car the cost is too much for proper height adjustable ones as I would like to be as close to stock height as possible due to scraping, my poor exhaust manifold is what scrapes most of the time.
Swapping out the roll bars is something I'm thinking about. Maybe swapping out the rear 16mm for a 21mm adjustable bar and going from there