[alasdair_]

>Of course this makes the game interesting and also explains why in real life the only sustainable model for economy is planning.

"real life" planned economies have done terribly so far, while price-based capitalist economies seem to have done a lot better.

>The planning starts from actually measuring/calculating the real demand.

Herein lies the problem. How do you measure "real demand" for an entire economy, without prices? Prices convey information about what is really in demand at a given time and without them it's remarkably difficult to get answers that don't involve guesswork or individuals demanding more than they really need.