Your proposed change is the very dangerous problem that you were worried about that made you implement a spending space cap in the first place.
The idea of just exempting certain items that you personally deem essential from the spending cap opens those products wide up for the market massive market manipulation you fear. Not to mention on the surface that sounds like an extremely convoluted and overcomplicated answer to the problem, and again subject to the whims of what you personally deem is 'essential'. Any shortage in country stock drops the supply index, so everything that the country consumes is essential by that logic.
Like it or not, wind power is the elephant in the room by your own design. That is far and away the primary reason for the need of this discussion in the first place, because you chose to tie its monthly income to the country in a way where the country is essentially a corporation and has to purchase the turbines to make their output farms. You didn't actually respond to any of the discussion points that I made in the other thread so I can't say anything new because it feels like you take a couple words out of a paragraph at random and choose them to respond to.
I could absolutely be wrong, but I feel that my suggestion for dealing with the contracts and spending space issue was much more straight forward than what you're proposing and just makes sense. There very well could be critical issues that I am overlooking, so by all means please respond. For those that missed the other discussion, the main proposal is:
Local Contracts (contracts made between a country and its state owned corporations) are not subject to spending limits.
The reasoning behind this is that the products the country produces for itself aren't part of the international market. The country determines that a product is essential to them, and they produce it themselves within the limitations of their population and worker education. It incentivizes growth while substantially limiting market manipulation.
Newer players and smaller countries absolutely have to be protected from the financial exploitation that larger countries could be capable of without limitations. Larger players should also not be punished just for being large. Some players have openly stated that they were at a point with their money where they had nothing to do with it. Players don't get to that point without giving you a fair amount of actual money and putting in time. Separating local contracts from spending space considerations essentially provides rolling spending cap relief as players grow larger on the stipulation that they are supplying the products themselves. Again, not common market contracts, local contracts. No matter what, the benefit will be limited by the country's population.