I want to buy this but I really like to customize my cars. Can you add decals and vinyls like in ProStreet on this game?

yes, but they cannot be seen during online play so there is no lagg. but thats us vinyls n decals

is the game worth the money?

If you want a challenge, get it. It is easy at first but later on, it put you against Zonda's and Murcelagos when you are in a skyline or something. The graphics are incredible compared to older versions of Need For Speeds. The game is based on Most Wanted.
There is also elements of Underground 2 with Outrun races and Highway races. Another good thing is finally the return of the helicopter. I have to admit that the pursuits are easy to evade when the helicopter goes to refuel (I think). I evaded a level 5 pursuit in about 20 seconds. There is good visual damage, but there is little or no performance damage to cars.

My criticisms would be, again there is a lack of visual customization. You can tweak the performance like prostreet but it is still behind on past games.

If you can see past these small annoyances and don't mind getting frustrated on later races, it is well worth buying