+1 on Takatsuki 300B
It comes down to your values. I replaced the OEM tubes in my Woo WA5. The difference was very profound. Tubes like Sophia offer an intermediate step up. If you want the best sound your system is capable of, then the Takatsuki are the way to go. But the level of difference will also depend on the rest of your system. If you have a very highly resolving system, the difference will be profound… if not then it will be less.
Also, what improvements would you get elsewhere if you applied $2,000. What is value of $2K to you? I have many interconnects worth more than that… pretty much a no brained for me. They sound glorious.
The fact you are thinking 0f putting some more money into a cartridge… makes me think perhaps you should stick with what you have and take a hard look at your overall system. Maybe read Robert Harleys book on High end Audio and consider the whole system. This might inspire other changes first… or not.