As a glock armorer, I would definitely be inclined to do this. I'm not the typical "part replacer" that was mentioned earlier in the thread. I was literally upstairs putting together a long range precision rifle I am building. I was just fitting the action to a bottom metal.
Anyways, it seems as though (I for one dont have any issues with any of my glocks and never had) that a light polish of the extractor will happen with use. So, I for one don't see an issue with polishing it but, it may shorten its life depending how much you remove. When we are talking 1000ths of an inch between working 100% and having erratic ejection, I'd just say be careful. A little will probably go a long way in terms of getting where you want it to be.
If your ejection is all over the place and you already replaced the extractor/ejector/rsa/ whatever else is said to be causing it. A little fine tune polish certainly couldn't hurt. I would do mine but, my glocks fire great, eject great, and work like glock perfection should. Maybe its my hand loads (wait did I just say that out loud)
Gen 3 23, Gen 3 21. Too many other firearms to list.
Certified Glock armorer.