I've had my ice screws sharpened a few times by Grivel sharpening machineGrivelsharpening machine. The screws after the sharpening machine seem a bit rough, but they do work fine, despite them usually looking a bit rough. Bursts need to be removed with a file, but other than that they have worked just fine.
However, the machine seems to just take off the material from the cutting edge, which means that the valleys between the teeth tend to get shallower.
Sharpening the screws with a file could produce the screws with more new-like shape, but sharpening the screws with a file takes a lot of filing, as the teeth need to be equally long. Which often means that you have to make all other teeth dull at first, then reshape all of them. This is rather labour-intensive and it is also easy to screw the angles up, which could produce fine looking screws with pathetic performance. However, I've seen some screws sharpened with a DremelDremel machine, which shaves off significant amount of time. Given that we have no Grivel machine available anywhere near where I live, I believe I need to give this a go. Keep in my that machine sharpening the screws is directly prohibited by screw manufacturers as it can overheat the screws, therefore ruining the tempering (read making the screw get dull and/or bend easier).