What to upgrade to?

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

By far the biggest improvement I have experienced (since my ears are not as sensitive as some other people I've known) are the best-engineered recordings I can find. Reference Recordings, various SACD's (not all!), certain vinyl (again, some good, some bad).
And-"maybe" try to pick up an instrument from a music store and learn how to play. A decent classical guitar is easy on the fingers.
In any case, We had a very mediocre stereo in my parent's living room when I was growing up. A Fisher compact system- receiver with a BSR turntable mounted on top and a pair of Fisher 10inch/2way speakers, skinny wires and basic interconnects. But- with a well recorded album (my favorites were Columbia/NYPO/Leonard Bernstein) the difference was stunning. If that's not proof I don't know what is. Atlantic records were excellent also (Led Zeppelin). Over the next several years digital audio engineering may get even better. Personally I don't know what to make of a turntable/arm/phono stage/cartridge costing more than (let's say) ten grand. I own a VPI Aries-I with a Benz HO-MC and a Luckaschek phono stage. It sounds great and I'm sure there's much better out there to be had, but I don't have an extensive collection of records (maybe 500 or so). Honestly none of the stores I've visited had a SOTA analog rig set up to play, so I've been on the CD-player road to better sound most of my 25-30 years building my system. One thing IS for certain- the VPI "killed" the Thorens I had previously owned. 
As far as a better system is concerned, it's also possible you might have to spend a LOT of money if you want a dramatic improvement instead of an incremental one. I found that out the hard way when I auditioned a $3500 Goldmund DAC over what I had.