What to upgrade to?

Maybe you can leave that money on the side and use it when something in your system fails. For now, why change the team that is winning?

OP.  I built an isolation stand for my vintage audio linear turntable.
step 1 go to grantie shop and purchase appropriate size remanent cost $10
step 2 go to local building supply store and    get a 2x2 chunk of mdf cost $10.
Step 3 find a yoga mat that no one is using cost $0
Cut the materials so they all match in size
sandwich the yoga mat piece between between the granite and mdf use construction adhesive to adhere them.
clamp it together and wait for the adhesive to set.
this works about as well as my symposium shelf under my vpi scout.
point is have fun if you're retired may as well have something to do, exercise your brain figuring out how to do it.

Bob, if I was making my last big upgrade, I would go out and listen to as many speakers as I can, and it doesn't have to be new. Speakers are usually the biggest and most expensive upgrade and effects everything played through it. Why not spend your savings here?

Since you've decided to upgrade to a new cartridge, this should give you a really noticeable change in sound. With your budget, I highly recommend adding a second arm/cartridge, I never knew how much I appreciated having the option of hearing a record played through a different cartridge until it happened. There's really not one perfect cartridge/component out there, so I feel it's good to have options. 

I have noticed a lot of professional reviewers own and highly regard the Devore Fidelity Orangutan loudspeakers.  They also seemed to favor analogue front ends with them.

I would upgrade my cartridge to either a Koetsu Onyx ($10K) or a Clearaudio Goldfinger Statement ($16K). To me those are the two best cartridges in the market. You will still have some funds left over for Harbeth 40.2's