Tried a fiberglass pen on the PS/2 port and I don't know if I'm going into the right direction.
There is certainly the scenario where I could make it worse 😀

You aren’t going to restore the lustre of the original coating, that’s long gone because of corrosion. Either do as you are doing and polish up to whatever finish you can best attain, or as you say, replace the parts.

I’d be concerned that if the shielding is that corroded, then the pins likely aren’t far behind.

I'd say, gently knock off the "mountain tops" with steel wool then go at it with metal polish.

edit: watch where little bits of broken steel wool go though, or any other metal residue. That's why to do it gently.

Green scotchbright, then magic eraser, then fat fiber pen loaded with copper sulfate solution for the replacement copper reaction. (Copper sulfate will readily copper-coat aluminium and steel surfaces using a replacement reaction. NOTE-- Please use DILUTE copper sulfate. Concentrated solutions will eat the underlying metal, heat up, and make volatile hydrogen gas. Dilute solutions will plate slowly, and more evenly with a more lustrous finish, which is what you want. It will be slow, and need lots of rubbing with the pen, but it will plate neatly.)

Follow up with tin plating solution.

polish gently with chamois or other similar soft buffing material.

Fiber pens should work for precise application of both reagents. Clean up with distilled water, avoid getting it in places you dont want.

Both are acidic, so be sure to neutralize with dilute baking soda solution, then distilled water.

(You can use the resulting pens to perform surface treatments on alumimium surfaces so that solder will adhere as well. Useful for aluminium sheeting being used to make new RF shields on DIY projects that need them. The seams can be soldered, and so can the legs of the resulting shield.)