Thanks for replies:
Long post was for reason - I wanted to provide the background, replying back and forth to posts takes more time that going through one long post.
Spark plugs are gapped, look fine and switching them around does not good - unlikely the source. Cables and even coils were switched as well.
O2 sensors - already have replacements but top one is pain to get to. Still, it's likely that observed signal issue are result and not the cause. Will replace them anyway.
Harness - last hope (and big problem).Today I retested all wires using multimeter (wiggled the crap out of them) but no dice. Not sure how to interpret results (the other day I definitely choked rpms when bending harness around the junction where it splits to FPS sensor). It's quite likely that the harness is put together from discontinuous wires that are soldered somewhere in the middle (wire colors don't match on both ends) - really bad idea as solder joint can break/fracture, corrode and start acting up (more so as the engine bay warms up). I still don't want to rip it apart but will do so if pressed. Also bad thing is that I could not find replacement at the junkyard - bunch of Focuses but all had different connector (main harness plug) even though the engine was the same (Zetec).
For now I zip-tied "injector rail" to fuel rail and the FPS connector (with broken clip) is tied to FPS. Tomorrow I test drive it on the way to work.
Weekend will be for harness work, I may get replacement FPS sensor at junkyard (to get rid off zip tie on this connector).
PCV valve - I will get one once I dealt with harness. What grease are you referring to? I could not find nothing other than dielectric grease (but I do see some grease on contacts). I did clean and air dusted all connections, never seemed to be really contaminated.
I'll post another update around the weekend.