This is a rather unusual query. I have seen one of my mates c200's, and the mesh / grateing that is before the MAF has been removed (or was never there) not sure which.

Would this cause any adverse affects to the MAF? Ive been told some model didnt have this in order to increase air flow.

in somebodys mind it mat increase the air flow, i believe it is mainy there to prevent any large debris either from the airfilter or that may somehow pass the airfilter from entering the engine,

Well i assumed the same that it prevents large debri. But i cant see any large debri passing the air filter. Interesting lol

Some eliminate it to increase air flow, but I have read that aside from filtering, the screen also improves air flow smoothness over the sensor which improves accuracy .. and I believe the MF is most likely calibrated with the sceen in place, either by design or individually, so I would leave it be ..

makes senese. On another note, He has also removed all the ribbing from the inside of his air box. Performance degrading, performance enhancing or waste of time ?

My take on that one is that the ribbing forces the air to be evenly distributed across all the surface of the fiter, allowing both better breathing and longevity to the filter in the sense that the intake air is not being sucked at the spot/ path of least resistance. but rather being tunnelled/directed across a uniform surface.
Better flow ??? not sure ... full use of filter surface .. yup..