Gold historically has been a useful portfolio component - but keep in mind that the launch of GLD in 2004 dramatically upended the market, and was a major (if not THE major) driving force behind the 2005-11 bull. Before that there was the Nixon-shock bull from 1971-80, followed by a 24 year bear market.
Obviously there was huge monetary expansion and significant inflation from 1980-2004, so there's no straightforward mechanical link between these things and the gold price.
The best signal for a renewed multi-year bull would be something like the launch of MMT, or another catalyst event which clearly shakes the foundation of the monetary system. Tough to develop much of a thesis otherwise beyond purely technical/trend measures.