Best Stereo Upgrade Value

I normally would not say Phono Cartridge but the new DS Audio Optical cart will render all MC carts obsolete. It’s that good.

Haven't noticed anyone mentioning power conditioner. EquiTech made every component I have perform much better. Single most effective tweak I've come across.  (not just any power conditioner will do that however.)

All other things equal start on cleaning up the power

This topic just goes to show you there are no absolutes in this hobby! The OP asks a question, and he gets almost entirely different answers from most people! This is why we see so many arguments in the forums. I guess everyone's experiences and ears are completely different.

Best upgrade?

Clean your ears.