@kaia
>why do you need to polish the heatpipes
It's not the heatpipes I polish but the contact surface of the heatsink.
Doing so create a much better heat transfers.
Thus heat get extracted much better from the cpu, thus less damages caused by electro migration, thus less energy needed by the fan too.

>I've seen guys use isopropyl alcohol and wipe away the old thermal paste with that
That's standard yes.

>does polishing really make a measurable difference?
Greatly in most cases. Around 10°C on average.