So RU is strategic spending.
No, it's capability.
Simply, look at the United States. That whole "sleeping tiger" thing that the Japanese mentioned during WWII.
You can't "buy" the US, you can't "sell" the US. All you can do, is develop your resources to a level that can become equivalent to the US.
The US has capital, manpower, know how, local resources. Even blockaded, the US is a force to be reckoned with. And, that force can be turned and focused, quite quickly.
Singer (the company that makes sewing machines) retooled to create rifles in WWII. That's capability, not money. They couldn't do it without the engineers, machine tools, machinists, and material.
At a very micro level, you and me, we can "buy" anything. We can "rent" engineers, machine shops, skilled labor, etc. At a national level, you can't really do that. You have to use what's in place. You have to develop your base. Strategic spending will, ideally, increase overall RU long term. More training, more infrastructure, more developed raw materials. But the spending itself is not an RU. It's spending to develop RUs.
Farm subsidy is another example. It's worth spending money to keep badly performing farms in place, because it's important to have an overall farming capacity, even if it is being underutilized. Easier to convert an existing, badly performing farm than it is to start up a new one from scratch should you need it. That idle farm is a measure of RU.