How Much Have Turntables and Arms Improved in 35 Years

Back in 1985 or "86 I bought a VPI HW-19 II turntable with an Eminent Technology II air bearing tone arm.  Both still work fine.  I have only had to buy and install a new wiring harness and air pump for the arm.  These were very good components in their day.  My question is how much would I have to spend to spend to audibly and substantially improve on their performance?
Add a zero to what you paid for the VPI/ET! But if you still enjoy the sound why change? Try a cartridge upgrade instead. 
I am a collector of vintage TTs. I have that VPI HW19 II. It is an excellent TT! With an excellent arm (like the ET) it is competitive with today's four-figure TTs. To do better you will have to buy a five-figure TT/arm ($10K+). A cartridge upgrade is more affordable!
Well kingharold, I have to admit up front that I am neither a VPI or a straight line tracker fan. But thankfully you did not get VPI's arm of that vintage. It was awful. 
Next time you play a record that is a little off center watch your cantilever closely in good light. You will see it drift to either side just before the tonearm moves. If you have a very stiff cartridge like a Koetsu you might not be able to see it. In some cases you will even see the cantilever wobble back and forth. The problem is the horizontal mass far exceeds the vertical mass. This is a problem all Line trackers have except one, the Reed 5T which unfortunately is $20 large. Brilliant design though. It is on my lottery list. This problem more than negates any benefit tangential tracking might have and severely limits your choice of cartridges.
So, in my mind something like a SOTA Cosmos with an Origin Live Enterprise arm on it would sound and function better. You would be able to jump up and down right in front of it with abandon and it won't skip, you would have a large choice of cartridges, and it will sound better. It also has a much more sophisticated motor and drive system than the VPI and a superior bearing (magnetic thrust system.) It would cost you about $17,000 which is an incredible value for a turntable of that caliber. If you wanted to go for broke get an SME 30/12 and slap the formerly mentioned Reed 5T tonearm on it for a tidy $65 large. Next up would be the Air Force 1 Premium again with the Reed 5T arm blowing a $165 large hole in your wallet. Frankly, if you are married the SOTA is the way to go. The Air Force is a sure divorce. If you are really lucky you might get away with the SME. 
King Harold
Are you looking for general forum banter, or looking to upgrade ?
If the later I would suggest to simply look to history.

The ET2 was put on many turntables when it came out.

As far as VPI is concerned that meant the HW19.

Harry W. at VPI liked the ET2 so much that after going through the HW 19 Mark 1-2-3-4 versions; his all new TNT was designed around this ET2.

Above linked Picture is credit from the "Indecent Proposal" movie.

These are facts, and the facts would suggest that your ET2 outclasses your current HW19.

So if you are looking for a turntable versus tonearm upgrade - turntable.

I will also add your insight, experience and familiarity with the ET2 puts you at a big advantage over others here who have never owned this unique tonearm.

Good Luck

Some arms like the SME V have not changed since first released in 1987.

I guess they never felt the need.

Turntables have vastly improved in the last 35 years.