Well, my MT is pure alloy. I am not one of those guys that spend thousands on alloy to simply go and trash it. I am not bashing my MT at all. I just like looking at all that Alloy while I drive it with care.
If you plan to trash your MT then go with the cheap plastic parts, easier to replace. If you are going for looks/durability and you don't plan to drive like a mad man, go with the alloy.
Nevertheless, the Alloy upgrades I mentioned are absolutley necessary.