Turntable upgrade recommendations: SME vs AMG vs Technics vs other

Air bearing tables are many and various - but all of them are expensive.

Mine is a DIY with air in all three dimensions. I did this with porous graphite bearing surfaces from the US company New Way, using the larger of their so-called thrust bushings. The best compressors for this purpose do not use oil (e.g. Juno) but are noisy, and should be placed in a utility room.

The air cushion is stiff and not a substitute for a suspension.

But the SOUND - quiet to the point of blackness. No noise at all. So clear!

I, too, have a VPI HW-40, but it is the last thing I would do is recommend it or any other specific turntable to you.  One thing to be very wary of, and this forum is a prime example, the correspondent who has a component they love and as far as they are concerned it is incomparable.  That is nonsense.  You need options and time to listen to differences.  There are a number of very good turntables available, you named some of them in your OP.  The hard part is to get a chance to experience them.  You ruled out Steve at High Performance Stereo out of hand without knowing anything about him.  I suggest you give him a phone call.  He is not a normal dealer.  He may be able to help you.  Call him. 917-208-4750.

Don't know what your budget is, but I love my Bergmann turntable and its linear tracking tonearm.  Makes beautiful sound and reduces issues with anti-skating, and other cartridge set up issues.

Contrary to what has be said earlier, I watched several Soundsmith videos this weekend and it was stated that the cartridge is the most important piece of your record playing pleasure.  Obviously you can't match very disparate pieces - arm, table, cartridge.  But it makes sense that that which has contact with the vinyl is essentially important.

No glitches to the air system for me.  Smooth, quiet, idiot-proof.  I see some reference to price in some comments, but your OP suggests you are looking at some pretty expensive options, and the Air Force V is something like $22k, then you have the cost of the tonearm.

To complete my thoughts, bearing noise in a turntable is not always recognizable. In a quality turntable, it can manifest as high frequency distortion on top of the signal, which appears to be clarity in the triangle or the harpsichord. But this is artificial, and becomes wearing.

When you hear an air bearing, preferably three dimensions of air, you hear an absence of this HF distortion, and the result may sound 'dull' - that is, until you realize that 4 hours have passed and you still want to listen. And you just don't listen to the other turntable with the conventional bearing. At all.

In a phrase: clear, but not analytical.

No maintenance problems with my setup. Several stages of air filtration solved that. 

But there's more to the initial setup than for a conventional turntable, so be prepared for that. I suggest that you listen to some turntables, including at least one high end like Walker or Techdas, and decide if it's worth it. If not now, perhaps in 5 years. Whatever. It's your money and it's your enjoyment that counts.

Good luck - and tell us how it works out!