Forgive me for stating the obvious here, just thinking out loud I guess...
So your O2s (both wide and narrowband) are reading lean, causing the ECU to dump lots of fuel, which is causing the plugs to indicate a rich condition... but the dumping of fuel is not changing the reading. It is unlikely that all the O2s would go bad at once. What really perplexes me is that an electrical issue (i.e. bad ground) would likely effect one set of O2s, but not both. So if the narrowbands went lean, but the wideband went rich, then you could check against the plugs to find out what was really going on, then chase down the error with the offending O2s.
So the reality is, so both sets of O2s indicate lean, then obviously you really are running lean. Has the operating temp of the car increased significantly? Have you checked signal from stuff like the ECT and MAF to ensure both are switching?
Paul.
