Using tinted plexi (or glass) is a matter of personal taste. Some old machines did it, others did not.
It's hard to explain what the benefit is, you just kind of have to see it. It deepens the colors, so the blacks get blacker, reds and blues get deeper, and so on. To my eye it also makes the picture a little sharper, because it eliminates some of the "bleeding" from one color to another. The non-tinted picture is brighter and more vibrant, but that isn't necessarily a good thing.
I go back and forth on whether I like tinted or non-tinted better, but in the end, I think I'd go with tinted. It's a more "arcade" type of look. It also has the added benefit of hiding the bezel, which I definitely like better.
-Jeff "etumor"