To clear up one misconception... simply sanding or running the car, no matter how much it sheds in the process, is no guarantee that they become round. Smoother, sure... but eggs are also smooth.
. A person with the rock steady hands of a brain surgeon can true tires on sandpaper, but the rest of us use a machine to precisely hold the wheels at a set distance from the sanding surface, ensuring that only the high spots get sanded off until it's round. If tires really did true themselves on the track, you'd have a whole lot fewer competitive racers using "fancy machines."
As far as "to what end" I will only say that this current conversation was started by your finding the new Revoslot to perform better on your new Policar track, and not immediately attributing that difference to traction. Even on a high traction surface like Policar, if the tires are not true, it will not be getting as much traction as it can. While you previously were happy with how your Revo had performed on your Carrera track, you are also happy with how it now performs on Policar, possibly more so. By making sure the tires are true, you'll get another boost in performance, even without any black magic treatments to the rubber itself.
In the end, we come up against the law of diminishing returns. The traction gain from Carrera to Policar will be pronounced. The traction gain from truing the tires will be noticeable, but not as pronounced. The traction gain of tire treatment above truing will be again noticed but less pronounced.
I have yet to tear down a Revoslot chassis to the same degree as you have, but I certainly true the tires if I'm planning to compete with it. I count trying to get a better lap on my track as competition.
If I'm just running the car around, and don't care about lap times and don't plan to race it with the guys, I'll pretty much leave it as out of the package.