I've ordered both front and rear reinforcement plates for my suspension refresh from Bimmerworld even though I know it may not be needed. Also new guide supports and rear shock mounts. Figured it would be lower a bit, possibly but highly unlikely more stiffer so to avoid damaging the shock towers in the long run seems like a good idea. I plan on keeping the car for years to come so it makes sense.
RTAB limiters are not exactly reinforcing the chassis per say. I found this link which explains in good detail what the limiters do for the car.
https://vorshlag-store.com/products/...iters-full-set
And you're correct about drilling a hole in the e46 reinforcement plates for the Z4 guide support alignment pin. But that's hardly a show stopper.