In this hobby we're always attacking the weakest link. Often that's a component, but once the components have been upgraded the cables become worth a look.
When i had a separate streamer and dac, the upgrade to a Tara RSC digital cable made a big difference. I had a good rca to my preamp. Once I upgraded to a much better streamer/dac it became worthwhile to upgrade the rca interconnect to my preamp. It further improved the sound by a large margin.
Same for preamp to power amp, as well as speaker cables after other system upgrades.