Replacing lower tier items with higher tier items. A change to cost formulas.

The general idea here is that once you unlock the next tier of something like vehicle parts, construction material, or lab equipment you no longer need the lower tier version of it.
Instead, the cost to build or maintain will be represented in the new tier of that component. But the amount that you need will be lower. For each tier above that one the amount of material you will need will be half of that needed for the previous tier.
For example, let's say you have a building that would normally take 80 tier 1 construction materials to build.
If you have tier 2 construction materials, it will only cost 40 tier 2 materials.
If you go up to tier 3 then it will cost 20 tier 3 materials.
And if you have tier 4 materials then it will only cost 10 of those.
It may require changing the amount of materials required for buildings, vehicles, and maintenance depending on the level but overall it would make for a better system in my opinion.