First off, spike and firebombs are just plasmas. They stick to you, you die. No need to have 3 grenades that do almost the exact same thing. Second, the DMR is the exact same thing as the carbine, and last I checked, the Carbine did not unbalance the game, so why would the DMR?
The armor abilities have to be found, and there will only be a certain amount of each one. There will probably only be 1 cloaking and overshield attachment on each map so I wouldn't worry about everybody having them.
I do agree with you on the Needle Rifle however, that dies sound very overpowered to me. Not too sure how they're going to pull that off...