One of the biggest problems with masks is that you can't get a good cheek weld with them at all. Now softer solutions like balaclavas or neoprene masks take care of that problem, but they have their own problems, mainly they're hot as hell. Personally I don't bother. No one in my group would purposely aim for the face and protecting against the occasonal hit isn't worth the inconvience of a mask.
Gloves on the other hand are definitely a good investment. Not only do they protect against bb hits but if you take a spill they'll protect your palms as well.
Kneepads are also a good investment. When you suddenly start taking fire, it's great to be able to drop to your knees behind the nearest cover without worrying about what's underneath you.