The Spending by Category Dashboard card's usefulness is limited because it only shows the top 5 spending categories. Everything else is lumped into "Other", and for most people, "Other" is the largest category and a large percentage of the total. This is a simple request to increase the number of categories displayed in the card. The fixed height allocated to the Dashboard cards leaves this one half-empty; using that space for additional categories would make this card more useful.
The easiest-to-implement approach would be to simply increase from 5 to a fixed number such as 8 or 10. A potentially better approach might be to include all categories with spending greater than some percentage, like 5% or 3% of the total spending.
While I understand that the Dashboard is intended to be a quick snapshot/overview of various aspects of your finances, and the development team has tried to keep things simple to prevent information overload which users won't use, this is a case where a small tweak to show more information would make the existing card more useful. Other Dashboard cards show more than 5 items; this one should too.