Having a fermentation chamber aka the good old bog standard fridge (with inkbird controller and a heat pad)are for me the big game changer(s). Stablising that fermentation temp will have one of the most siginifcant impacts on flavours if the rest of your process is correct. I really notivce the difference now and I'm brewing at every opportunity as I'm much happier with the final beer in the glass. Knowing that the yeast is working at its optimum temp and the ability to do diacetyl rests etc if required offer repeatable and measureable changes in your process which is invaluable.