Many archaeologists point out that the mundane, everyday objects turn out to be more informing than golden jewels. Huge amounts of information were lost at digs in a pursuit for grave jewellery rather than doing science.
If you find a broach all you know is they liked gold and traded for it. If you find a nit comb, you know they had nits, and you may find DNA and trace diseases, and the comb may be amenable to chemical analysis to origins. (I know that analysis of gold and jewels is also informing, so this is more said for dramatic effect than truth, tradelinks about economies thousands of kilometres apart have been found in the chemistry behind jewels. The point is that mundane objects like spice speak volumes. Where does mace (nutmeg skin) grow? How does it get to the Baltic in volume? Henbane is useful in dying and medicine and as a hallucinogen. Which purpose did it fill?)
For consolidation of power. I guess most historical occurrences of "insanity" were simply attempts of elimination by deliberate poisonings.