I will just put in my opinion on this one. 1) If you need it get the security system, I guess it depends where you live and how worried you are about a break in. I don't know how the system compares with aftermarket but I also don't know how different systems are in general. 2) Cap as in shell? Shells are nice and if you can get it for a good deal with the sale then that would be good. They might overprice it when they add it though so you will have to compare the price they would add to what a new one would be. 3) The stock skid plate isnt bad, I have railed mine of many rocks and it is holding up. Eventually I think I will get a different one but stock they are alright. 4) From what I know I think the running boards that would come factory are worthless. They are nothing like rock sliders and dont really do much for you. 5) Dont know what you mean by dimming mirrors.
That is my two cents.