upgrade path

Check out the Basis 2001 with the Graham 2.0 on AgoN that would be a great next table. The Graham arm is very adjustable, you'd learn cartridge set up and adjustment and the Basis 2001 with its suspension isn't as susceptible to vibrations so isolation is not as difficult as with some tables. You have two very good components together, and he's open to reasonable offers!!!

vpi classic is the best way to go. The vpi can then be upgraded with the ring and other tweaks. Great sound and value.

The 1200's a great table. Think about upgrading your phono preamp and cartridge.

You have to do some search and then decide for the right mods. I mean real upgrades (bearing, electronics, plinth) and then look for a copper mat, a peripheral ring & stabiliser.
Are you shure that you can mount the SME 309 on this armboard?
You must first measure the pivot to spindle distance & then you have to find the corresponding effective length. Then you can search for arms with exactly this eff. length. Also, take care for the proper match between your current armboard & the potential arm base (of the new arm).
If you can avoid the fixed arm base and you can construct a new (outside the chassis) on a heavy surrounding plinth, then I think it is better to look for the SME 312S.
I'm warning you: The transference to a belt drive is a very traumatic experience that you are going to regret.
Leave the luxury marketing objects to some fashion victims & proceed carefully with what you have.
Trade your AT440 for the best AT you can afford and stay to MM, otherwise you must have very deep pockets for equal quality MC & a worthy phonostage (very few in the market).
Good luck

George

Samhar made the best recommendation

OK!
I always prefer to advise moneywise.
Think of a Denon DP80 with SME 312S or Technics SP10Mk2 with a Jelco SA 750 LB 12". Audio Technica AT 150 MLX is always a great company. Or you can go for the Dyna DV17D3 with Dynavector P-75 mkII Phono Pre Amp if you lust for an MC path.
Yes there are more expensive but not always better (mostly different approach) front-ends. To justify your expense you must hunting even for the best RCA plugs, special cables, tight synergies among every tiny & impossible things you can never imagine in the rest of the chain. A very sensitive balance. But the worst that comes with this elevated quality, is that, it has a very closed & specific circle of friends with unique demands that force you to obey otherwise refusing to charge the emotions.
Somehow the "system matching" that we use to say so often looks like a deceptive thing that we agree to accept it reluctantly by this very fact of the resulting characterisic personality that added to a product almost accidentally by the designer's mess it up.
I think it's great for you that so long you did not throw out your money. Do you think it's time for you to dance with the rest of us & experience the bitter taste ?
(round belt & heavy Aluminium, versus flat belt & Acrylic, versus thread or tape belt & composite resins, together with flea, toy-like motors & fancy appearance)
You can reach a level for shure without enter to this circle of the endless inaccuracy and uncertainess.
If your appetite permits, wait a while and save up for something that no salesman can change your mind for the new & improved. But always keep the thought that in our days audio is mostly business (and a dirty one with deep corruption, mafia & worthless upgrade efforts by their victims).
Among my journey to hi-end the most beloved set-up was the DP80/SME V/Grasshopper III M. The best performance/price and the most easy to use with absolutely no maintenance.
Twenty years after and I still miss it.
Take care

George