sorry Johnnyboy but I still haven't got to the bottom of this probem.
Few months ago I went back to the Alfa specialist to replace the fuel injector on cylinder number 2, as I was so sure that it must be causing the misfire as everything else (coil packs, spark plugs, MAF, air filter, battery - O2 sensors were replaced 1.5 years ago) was brand new!
Well, the injector was replaced and...nothing, that little misfire/stutter/hesitation was stil there. As a part of replacing the injector, the engine manifold had to come off, so they gave it a bit of a de-carbon clean as well, and the results were really noticable - theres no more of that lumpy idle, and the engine revs much more freely after 4000 rpm, but like I sad, that hesitation is stil there.
They said the voltage in the car does tend to drop considerably when the engine is under load, especially when the other electrical devices or on (lights, air-con, etc) so now they think it must be electrical.
They advised me to book in the car again, as they need to spend quite abit of time monitoring the voltage in the car and seeing what exactly causes it to drop (they said they have to make some sort of electrical jigg that connects to various electrical connections and wires around the engine, so they can monitor the voltage variation of pretty much everything) and it is quite time consuming.
I'm actually booking the car in for next week, so I'll let you know of the progress