well i dont think paying money for a game is worth it...at the end it is something virtual .. if u have extra money ur welling to spend just spend it on sth more usefull like saving money for a new ipod or sth... or even donating this 10 $ for the starving african children u know u could save a life of a child with only 10 $ just think Wise before u spend money mate.. at the end it is ur money do what ever u feel like doing .. cheerz
You can choose at your own will. If you are into the game a lot, then I'm sure spending a few cash on the game for some special benefits won't do any harm. I, myself, have spent about over 100$+ into CF getting ZP.
You can choose to purchase the whack temporary guns, or go for a shot at ZP crates.
It's similar to console games such as Call of Duty. People purchase map-packs and other DLC since they enjoy the game. Having more features will add oil to the fire, or in other terms, make it more enjoyable than it already is. Picture it like that.