An aspect of restoration that is much misunderstood is polishing. There is moderation in all things and it should be applied to the final stage of restoration. I’ve seen many pens that have been machine-polished to death and beyond, producing a hideous glaze that bears no resemblance to the original appearance of the pen. Note: I don’t condemn buffing machines. I have one myself and it’s useful for reducing or removing scratches and nibbles.
I’m not one of those restorers who tries to return a pen to its appearance when new. That isn’t possible with most old pens, nor, to my mind, is it desirable. There are several restorers selling their pens in eBay who practice this type of restoration and do it well. Of course their starting point is an old pen in near-pristine condition. You’re unlikely to succeed with a scratched or faded pen with worn trim. You can’t make a silk purse out of a sow’s ear. It’s best to aim for an attractive appearance that acknowledges the pen’s long use.
Gold plating, in its various kinds, endures better on some pens than others but a well-used old pen will always show wear even if it’s only on the ball end of the clip. The plating on 20s/30s Parkers and Sheaffers lasts better than most. Other pens, even high quality ones like Waterman and Swan often have some brassing. What do you do about it? Re-plating is out of the question for everyday pens. Even for more expensive ones it may not be appropriate as it’s very hard to colour-match gold plating. I would suggest that heavily worn clips and levers should be cleaned and then left alone. Constant repolishing will make them look good temporarily but every polishing removes more gold. There’s little to choose between metal polishes; they all abrade the present surface away and present a new one. Semichrome is well regarded. I use a rouge cloth.
Finishing hard rubber is something we could argue about all day and long into the night. To reblack or not? Up to you. I don’t do it and I don’t plan to get into the pros and cons here. Even faded hard rubber polishes well and shines even more, the more it’s used. It’s a very rewarding material to work with. If they aren’t too extreme bite marks and scratches disappear like magic with a blast of heat. Not so much celluloid or casein. That sort of damage requires work with the Novus three-part polish. Otherwise, all those materials were a good choice for the manufacturer and shine up well. If I don’t have to repair the surface I just use a Sunshine Cloth. It’s all you need, really.
Finally, and I admit I’m a bit of a bore on the subject, don’t put wax on your pens. Renaissance wax and Cornuba both contain chemicals which will harm pens in the long term, especially celluloid. Waxes discolour through time and are very difficult to remove completely.