My apologies, I guess that came across a bit harsh.
Top plate:
There are 2 parts that can be referred to as a "top plate."
1 is on top of the center differential, and it stiffens the differential mounts and provides a retainer for the brake cams. Some truggies use carbon fiber there, but even with bearings on the brake cams, the carbon fiber wears faster than aluminum. I replaced the carbon one on my previous Jammin truggy with the (CHEAPER!) aluminum one from the RTR version because it is more durable. (the aluminum one is heavier of course...) That might be what you are referring to.
The other is the part that connects the top of the servo saver and idler arm and the front chassis brace to the front bulkhead (differential mount) and in some cases like the Mugen for example also mounts the upper suspension arms. I would have happily replaced the carbon fiber one on my old MBX5 ProSpec with an aluminum one, because I broke several of the carbon ones.
The reason to replace either of those would be for more strength or durability.
As for a camber plate, I'm sorry, I have no idea what they are referring to. On all of the decent quality truggies I am aware of, camber is set by adjusting the length of the upper control arms. Now, possibly they mean TOE plates, which would be what holds the rear end of the rear hinge pins... you use different ones to change rear toe-in. Changing from the stock plastic (On most trucks) to aluminum would be done for durability. Some of them have adjustable inserts so you use the same plate but change the inserts to change toe.
Hope that is helpful.
Now... what are you trying to accomplish? What kind of truck do you have?
(EDITED
I did a search and I found what I THINK you mean on the top plate, and based on that I can guess what the other is. They have a plate to use with RC setup stations (like the Hudy one for example) that is longer than the one for 1/8 scale buggy. It is used to tell how much front toe you are running on your truck... WITH the regular alignment station parts. It does nothing by itself.
As for the camber plate... maybe it is like the "quick set" camber guages which allow you to measure camber with the wheels on your truck. It isn't as accurate as the real alignment station, but works pretty well... well enough for most purposes.