Cleaning tracks

I'm using the old 9V train system where the motors are getting electricty from the tracks. Since end of 2007 this is a discontinued product line so I have to buy used parts. The problem is that I need good electric connection because I'm planning to build a DCC system where it's not just the power but also digital signals are sent through the tracks. How can I clean the used tracks?

Lots of old tracks need cleaning

Polishing set

First I tried with alcohol based cleaning product. It didn't make much difference. Then a friend suggested polishing. The result is clearly visible. The question if the wheel friction will be effected or not...

Before and after pictures. In real life the difference is more visible. The small polishing pad I used for testing got dark from the metal.