The wealth cap is fine for a stopgap solution for the sake of getting C# Aurora tested and released. For a longer term solution, we need to define exactly what wealth *is*. We can safely assume its not just money, but rather represents the entire industrial capacity of your empire, all the non-TN manufacturing, services, etc. A "Finance Center" is not actually a New York Stock Exchange, but rather a commercial district where small business can flourish and provide goods and services to the public as well for state consumption. It would also reasonably include all TN minerals not in state hands (both % from your mines as well as CMC's that you dont buy).
If we see Wealth as "Industrial Capacity", it makes sense that you can't save it up. If there is a company that can build toilet seats for 4 spacecraft in a year and you build 0 spacecraft in a year, it does not follow that you can now build 8 spacecraft's worth of toilets the following year, you can most likely build 0 as the company has gone bankrupt due to having no income for a year.
You can conserve resources to some extent, building up stockpiles, but there is a very low limit to how much of that is feasable. The economy only functions if it flows.