The relatively small amount of money I have put into my espresso setup has made a noticeable difference:
* Breville Bambino
* Niche Zero
* IMS 20mm baskets for Breville portafilters
I can get within spitting distance of most third-wave coffee shops most days.
Still a lot to learn but I can tell I'm nearing the point of rapidly diminishing returns. I'll probably look to upgrade the Bambino when it dies, but I'm not really jonesing for much more at this point.