Have a read of this then smart arse, they've been used in motorsport for decades.
http://clubgti.com/forum/showthread.php?t=223608
And if you took your head out of your arse and read the thread properly, you'd see that the Motorsport plates are fully braced...nut just a 10mm plate bolted on.
The comment stands...that thread also discusses fully braced rear beams - for stiffness. I'm fully aware of the thread...I have a fully braced rear beam on the back of such a thread.
Oh, well then! You must know what you're talking about! Just because its all braced in motorsport application doesn't mean it's necessary for road use. It's obviously gonna be under much higher stresses in motorsport. Have you ever felt a 10mm thick plate? There is NO way that it will bend lol. As for the bolts, how do you think stub axles are held on in the first place? It's no different! As long as they're the right tensile there's no reason it would be unsafe.
Besides, the plates that James has on his mk3 are a tried and tested product from a reputable company in the US.
There isn't a better way of keeping lots of suspension travel and being low, unless you get hold of some custom length strut bodies. Damping adjustable coilovers don't make a blind bit of difference when you're sat on the bumpstops, don't you thick race teams would have thought of that if it was the case?