Tell about your experience with your old Audio-Technica SL-1200s..

I've had an SL-1200 MKii for about 40 years now - did some KAB upgrades, added a Hana SL cartridge (have a Shure V15 MR Type V as well with the original and a new JICO stylus).  Was thinking about an upgrade to a GR or something else around $2k-$3k and wanted to know, if you came from an old 1200, where did you go from there?  Did you go anywhere?  What did you gain from your next turntable?  Did you keep your old one and are you currently using it as a lazy susan?   I had been considering a tonearm upgrade as a possible option but it looks as if the SME and Jelco arms are disappearing fast or are going for crazy prices.  I understand that if you've never had one, you have no basis on which to make a comparison, but if you have something that knocks your socks off that doesn't require a second mortgage, please share.
Seems you've got the tt's naming conflated, and therefore confusing.  Do you mean a Technics SL-1200?  Or an Audio-Technica LP120?  

Here is a story:

I still have a pair of upgraded SL1210 mkII in my second system, I bought them in 1995. After all those cheap Ortofon, Shure, Grado (MI and MM) cartridges I finally bought Technics 205c mk3 then mk4 and I was blown away! I tried those rare Technics carts rebuild, re-tipped, with JICO SAS Boron and finally with original stylus (it was the best). And it was a huge impact to start digging for a better cartridges, I tried modern LOMC (it wasn’t better).

When I was ready for upgrade I decided to buy Technics SP-10 mkII and it was HUGE upgrade over my old SL1210mkII with all the tweaks. My choice of tonearm was EPA-100, but then I bought "12 inch Thomas Schick and finally Reed 3p "12 inch.

Then I discovered Technics SP-20, here you can see my SP-10 mkII and SP-20 (black).

After several years of searching and trying many direct drive turntables I ended up with this PD-444. I bought a pair and never looked back, clearly my favorite turntable. But my interest in vintage Direct Drive motivated me to buy Victor TT-101 and Denon DP-80.

I had to sell all my Technics (SP10 and SP20 series) turntables to raise funds for other turntables.

P.S. If you want to try something much better and DIFFERENT then I can recommend SP-10 mkII with EPA-100 tonearm (as much better turntable) and Denon DP-80 in original plinth with DA-401 tonearm as something different and better. Those are reasonably priced, so they are best bang for the $$$.