It wouldn't be too hard to replicate certain parts, like hinges and whatnot, but trying to make something like a display bezel or molded case part would be a nightmare. Most machining done these days is subtractive, as in you start with a billet of material big enough to contain the entire part, then you selectively mill away material leaving your part as the result. You also have to consider how you will hold down the material securely enough to mill it while still being able to get a cutter into all the places it needs to get without cutting into your fixture or the attachment points. Many times you need multiple fixtures to mill a complex part in multiple separate operations, and one mistake along the way means you toss it in the scrap bin and start over. Figure several hours to draw up the part in the CAD/CAM software, cycle time anywhere from 10 minutes to over an hour, all of that at a typical shop rate of $85/hr. Then on top of that there's the cost of material, which can be pretty significant if you need to start with a big slab to mill out something like a bezel.

Bezels and plastic case parts is the sort of thing a 3D printer would be well suited for. There is still a very considerable amount of effort in getting the part drawn up, so unless you know someone who does that as a hobby you will spend far more than the current value of these machines.