My setup is:

Thorens TD-150 -> ZP3 -> ZROCK -> Torii Jr -> HR-1

The TD-150 is upgraded a bit, RB-202 Tonearm, Cardas Wiring Upgrade, New Plinth, MusicHall Cruise Control 2.0.

So I currently have a few things going on:

1. Footfall issues with the Thorens TD-150
2. Belt Slipping on Startup (Annoyance Mostly)
3. Undecided if I want to move to a 2M Bronze to a MC Cart (Hana ?)
4. Upgrade tonearm to Jelco 750D?

My main questions are:

Is it worth upgrading the tonearm/cart on the TD-150 or should I look at a different table?

Is something like a MusicHall 9.3, ClearAudio Performance, or GEM PolyTable going to sound significantly better?

All of the above I would have with a MC cart, is the move to MC going to be groundbreaking?

Any insight would be very helpful, I am reluctant to put more money into the TT due to the footfall issues. I have never had an issue with my previous non-suspended designs. That is why I am intrigued by the PolyTable.

Adding isolation might be throwing good money after bad.

Thoughts?

I'd like to second Syd's recommendation for a spring platform under the TT (all components, actually).  I use a homemade one under mine and the TT already has Isonoe footers (which are very good isolators).  I can pound as hard as I can on the main TT support (very solid, built-in cabinet) and I can't hear it through the pickup, let alone make things jump.  One thing about spring isolation to consider is that pure springs alone still allow higher frequencies to pass through into the component.  I always top my platforms with a compliant material to damp out the frequencies let through by the springs.  That's why the combination of springs and Isonoes work well together.

My understanding of the spring platform is that they don't damp-out or "drain" away vibrations but rather they don't allow frequencies outside of the fundamental vibration frequency to pass through in the first place.  I have other tweaks to help with air-borne vibrations but they don't seem to be a factor for me anyway.

In my opinion, when induced vibration is eliminated at the source, a "poor" table can become a great table.  First isolate the table to see what improvement you get in sound with your existing cart.  I use an Ortofon Jubilee on a Technics 1200 Mk2 table but with all of the table mods I feel justified.  On a stock table with no isolation I think I'd be wasting money.

I'm not familiar with the Thorens table design but if the suspension isn't tuned right it could exacerbate rather than help with footfalls.  Oh, and buy a new belt.