It's been a couple of weeks since I installed the new V-wheels, and it completely solved my biggest gripe with the machine, namely the constant bed leveling. Now I only have to re-level the bed if I physically change something on the Z axis (i.e. adding PET tape or fixing the Z rods). What also helped is that I now use a feeler gauge to level all four corners to 0.1mm exactly, then use MANUAL_Z_HOME_POS in Marlin to set Home to 0.1mm. With this I finally have exact and repeatable Z coords.
In the meantime I have also discovered the magic of hairspray on a heated bed, what a difference a little spray makes. I didn't have to find anything specific, I use "Finesse Keratin Protein Firm Hold Unscented" on top of a layer of PET tape applied to 3mm borosilicate glass, and it works amazingly well.
I am at the point where I can almost reliably print any PLA object, but it is obvious that I am suffering from the infamous Z-wobble common in the design. I was under the impression that the redesigned Z axis brackets would solve this, but I guess the threaded rods supplied by ATI are too bent for the Z travel to be even. I have ordered some ACME threaded rods to replace them.
I mentioned earlier that I switched to the Azteeg X3 with the new TMC2100 drivers, and that is an amazing combination. At 12V the steppers were emitting a very uncomfortable high-pitch noise (even when not moving), but that was completely eliminated when I switched over to 24V. The machine is almost totally silent (no stepper noises).
My main goal when I chose the ORDBot platform was that it seemed like a good compromise of price vs performance, however considering the amount of time and effort I put into this, if I were to do it again, I would just buy a PrintrBot Metal Plus. At the time the import charges were quite prohibitive, but the prices were significantly reduced a few months ago. A friend of mine ordered one and was up and running after 30 minutes... and after six months I am just starting to print reliably.

I guess that on the plus side, I know a lot more about the machine, and can deal with problems much more effectively, but I wasn't expecting to buy yet another hobby.

Of all the things I bought, the only parts that have never failed me were the EZ Struder and the E3D v6. These two items are completely worth their weight in gold, and have worked reliably from day one.
Cheers,
Ben.