What to upgrade to?

What about your amp?

Speakers will change the sound more than anything.
Have you ever heard Sanders ?

Good luck!

I owned a pair of Innersound Eros 3 which was his company before he started Sanders.  They were outstanding speakers and I am sure his new one's are much better.

Bob — Just came through a similar dilemma (in my case, a few extra bucks to spend; nowhere near retirement; and pre-Covid by a few weeks).  Existing system was very strong, but I decided one can always have a better cart and phonostage, and — other than speakers — those two items can make a bigger difference than a TT, assuming your existing TT is high caliber already, and assuming you spend a good percentage of time listening to vinyl.  I went from a Kiseki Purple Heart to a Lyra Etna and from a Gryphon Sonett to a Audio Research REF 3 phonostage.  Blew my mind how much improvement that brought.  The ARC can be found used and they’re basically bulletproof other than the tubes.  I highly highly recommend this option.  (Also, I’ve skipped many of the responses above, so apologies for any repetition or missing something you may have clarified.)  

If to look everything looks solid.
Only one issue - you have only one tonearm. IMO another tonearm with higher eff mass is the way to go. So to upgrade you have to have second turntable or sell this one and get another one with 2 tonearms. 

Chakster,
Thanks for your reply. I have looked at Zu and my amp would work perfectly. Btw I purposely didn't list my table or speakers because they both are excellent. I just would like to hear other people's take on which made better sense to upgrade. Some say source is #1 others argue speakers make the biggest difference. Thanks for your recommendation.

You're welcome. It's definitely worth to try ZU and simply return them with no loss if you don't like it. 

Speakers definitely will make bigger difference if your turntable/cartridge/tonearm already very nice.

When i upgraded from traditional (2way) Dynaudio speakers to Zu Audio Druid mk4 i was shocked. Because ZU is different concept, their own driver is super efficient, this is full range driver, NO CROSSOVER, only high pass filter for super tweeter. This is the most dynamic system i ever heard and it's a pleasure to use Zu Druid even on very low volume (if needed). Also my power amp right now is Yamamoto A-08s with 45 tubes (only 2W power) and preamp is passive Pass Aleph L. It's so easy to drive ZU Audio Speakers even with 2w amp in relatively big room! Amazing. 

Try it. maybe you will discover something completely new if your current speakers are not full range type. 

If you like it you can always add Zu Audio SUB, there are few excellent models look here. 

Another speakers that impressed me were Tannoy.