Upgrade my older Linn Sondek or move on?

Ha-Ha, I had two friends back in Colorado. Both with Quads, MV-50's and PV-5s. Both ran Denon MC. One a Linn, One a SOTA.   Now, the sound from both was fantastic, but they would argue endlessly about their tables!  

The biggest improvement I heard on a table was at Transcendental Sound in Denver. He put his table in an isolated box on a suspension.  No feedback. Really improved midrange clarity.  If I remember, he ran a Panasonic strain gauge cartridge powered by Jeff Roland's power supply. Jordan module arrays on giant sono-tube woofer cabinets. 

You mentioned a Well Tempered.  My own TT journey took me from a Linn LP12 /KMAL to a Technics SP12 /AT, to a SOTA Sapphire/ Premier MMT.  this spanned 1975 to the late 80s.  I then got a Well Tempered TT/TA and enjoyed it until a year ago.  No springs, no feedback, no static buildup, no endless tweaking.  Stress free listening….don’t dismiss it!  I now have a Thorens TD1600 and AT-LOC9XML, and it’s pretty good, but I am disappointed with the arm.  

The LP12 is a great TT owned one many, many years ago, had the best PACE to the music than almost any other table at the time. Biggest issue was it was tweaky, as many have already pointed out, and the top end was rolled off as well as the bass bloated. I moved onto a SYD (Simon Yorke Design) which had the PACE & Rythm but took care of the top end and bass issues of the LP12. Yes @mijostyn is correct regarding isolation, almost a MUST for any non-suspended table. Once heard it becomes a eureka moment. (Dealer disclaimer, we are the importers/exporters of the Vibraplane and have now sold over 6,000 units world-wide). The MinusK actually goes lower in isolation than a Vibraplane but has other concerns but is another excellent isolation platform not to overlook. 

Recently I was at @mijostyn home and had a listen to his SOTA and as he stated, when he placed a seismograph application from his phone on the platter there was ZERO response. GREAT sounding system BTW, a most enjoyable experience. 

FWIW,  I chose a different tack for a lot less money and it's a nice affordable turntable.

I bought an old SYSTEMDEK IIX (the poor man's LP12) in good working order,  ordered a NOS Jelco 370 oil damped  tone arm  from 1984 (period correct for the circa 1984 llX).  I'm going to find a phono cartridge  commensurate to the rest of this TT and hopefully be set for many years. 

Just some food for thought. 

So that’s what you’re supposed to do with a TT!!!

Put a seismometer on it. No one ‘splained that before.