I had the same problem last year, and in addition to what you did, I also:
- fixed clogged flame trap
- replaced fuel filter and check valve
- did a fuel treatment
- replaced air filter
- replaced O2 sensor
- verified Engine Coolant Temperature sensor was accurate

My cold starting is significantly improved this winter (ran a little rough for 10-15 seconds twice). Either the plugs/wires/cap/rotor (which you've already done), or one of the above items (which you haven't done) was the factor - or a combination of them. The items above are in what I believe to be a rough significance order. Another thing you could check (which I didn't really verify) would be to check for intake vacuum leaks. If there's more air getting to the intake than the AMM knows about, your mixture will be lean, which is a more significant problem when it's really cold.

There was so much moisture in my crankcase, that the oil dipstick and spark plugs were rusty! My fuel filter was so clogged, I couldn't blow through it; it seemed air tight. I've read that deposits on the intake valves can soak up fuel needed more on cold startups. I don't think the air filter O2 sensor were significant factors, and in my case, the ECT was fine