I saw this idea posted in the "suggestions" forum some time ago, and didn't give it much thought.
In hindsight though, maybe it deserves another go.
The suggestion was to increase the IC level in most provinces by a factor of 10, but leave the 1 IC provinces at 1 IC.
This means that the 1 IC provinces can still build anything they want, but have only minimal effect on the overall production level of the country.
Of course, all resource levels, all build costs, and all research costs will need to be bumped up accordingly.
Since there is effectively 10 times as much IC available, you would also need to bump up the supply usage by a factor of 10.
It is my understanding that all these things can be modded.
The down sides as I see them revolve around the following.
The resource pools can only effectively hold 1/10th as much due to there being a limit on their maximum size.
It basically becomes impossible to effectively increase IC's anywhere (ie it would take 10 years to increase the equivalent of 1 IC now).
I don't see either of these things as necessarilly bad, since I believe there are too many resources available anyway, and pre-war production levels are also too high IMO, so this point sort of evens out.
The only other real concern is that other province improvements are signifcantly reduced in price, if not in time.