I don't think the course of the war would've changed just by having more tanks. In the Russian campaign, they could've used more trucks and halftracks so the troops could've kept up. .
Rommel sure could have used more armor but I don't know if the outcome would be different.
Concentrating on just a few models would have helped,say the MK IV and maybe the StuG series. They would be on equal ground with whatever tanks the Allies fielded. The factories would have been under constant bombardment from the air.
The Allies did'nt have that worry[for the most part]. In Europe, German armor was under attack from the air as much from the ground. Having more tanks would make for longer columns.....juicier targets for the tabos. Without an Airforce to watch out over them , more tanks would'nt have helped much.
Keeping well trained crews in the field might of been a problem as well.