It's very nice of you to single me out, but quite honestly, it's not justified, I don't have the experience and am just trying logically to think what the problem might be and suggest that.
You are quite right though that the real experience you need for this car resides in the States. Generally that is not the case, since for very many cars, the UK is the authority. I'd be willing to bet that if you could post these symptoms up on a UK board (say for the supra) the experts there could have a good stab at diagnosing the issue even not knowing the car
Its true what you say about the Supra boards, but they have the benefit of having had the car available to them for what, 10 years plus? We've only had the zed for five years and the earliest cars have only been out of warranty for two years, which is not a massive window of opportunity for people to experiment with FI. There are the obvious exceptions though, yourself, Baptist, Val ( ), Spill, etc etc
I think as the price of the car drops below £10k you'll find all the FI junkies come out of the woodwork as the zed becomes more attractive to ex supra owners and the like.
Give it another five years or so and I reckon there will be plenty of TT'd zeds about and maybe then the uk FI will be self sustainable without needing to refer to the yanks when things go wrong.