The biggest difference I see between my first real system and what I have now is overall better clarity, refinement, and coherency, with a much bigger and better defined soundstage. There are simply fewer things contributing to the smearing and grunge many of my earlier components were riddled with. Power supplies are better, parts quality is better, isolation is better, the synergy between components is better, and there are fewer weak links. Many of those weak links are unseen, but are usually what hold a system back.
When I started, I thought lower THD and more watts is what made a system better. For me that wasn’t the case . Better basics across the board, and a better understanding of what it should sound like help me plug away at refining what I have.