jfd: Let me put it this way... "Death to the Greddy box!!!". I spent/wasted too much time and money on this same problem 5 years ago and don't have any more patience for it.

To answer your questions, yes on the VAFC/check valve/FMU adjustment issues, and no on the ditching the FMU - it's there to up your fuel in response to increasing boost and you didn't mentioned any other way to do that. Just upping your injector size would only account for an across-the-board increase in air flow, like if you had some serious head porting/engine work or swapped in a B18. Also, your A/F guage going crazy is exactly what happened to me back in the day.

I don't think you wasted your money on an in-tank pump. I've been running one for ~5 yrs and have run as much as 10PSI with it (~8.5 regularly) and haven't had any problems (it's a stock D16Z, after all). You will need to check on the pump's ratings to see if it will support your horsepower goals. Some people want to run in-line pumps and don't check if their HP needs have some amazing fuel requirements (ie, don't build a fuel system for 500HP when your engine will only make half of that). A good in-tank pump will satisfy almost any D16 fuel needs you have for a relatively stock engine.