The USSR did have a plan to attack Germany. This was largely because they believed in fighting on enemy soil. It wasn’t put into action because Stalin was paranoid about starting a war with Germany. When the generals got wind of the Barbarossa plan they urged Stalin to attack first, but he dismissed the warnings as British plotting.
The main reason the Soviets did so badly in the face of the German attack was that their entire philosophy AND preparations were to fight an aggressive war; they were not prepared for, or ready to adapt to, a defensive operation.
http://www.vho.org/GB/Journals/JHR/16/6/Bishop22.html
http://www.bytwerk.com/gpa/signal-1aug1941.htm
One problem game designers have to deal with is the difference between a country during peacetime and on a war footing.
Neutral countries of course have small defence forces; but these don’t increase every turn as the nation spends money; they have reached the maximum level the country can reasonably afford to spend on maintaining and upgrading defence.
Likewise, every major power should have limits on military spending in peacetime viz:
A limit on income spent per year. This will be considerably less than the wartime total.
A maximum peacetime establishment in units, probably divided by army, navy, air force. They can upgrade say a destroyer to a cruiser, but not increase total units (or “tonnage”?)
A maximum number of units maintained in wartime, determined by IPC levels; i.e. a country cannot withdraw to defend its capital with a huge force unless it controls a considerable “hinterland” income to support these forces.
So, how to reflect the fact that the Soviets had a relatively low output of units while restraining them from just attacking first turn to wind their economy up to maximum? What is their incentive NOT to attack, when they know (unlike Stalin) that the Germans will attack them eventually in any case?