Someone once said "A motor car is not a chainsaw" - engine management systems are seldom designed for throttle response off-idle with the car stationary
So don't worry about odd characteristics when idling in neutral - delayed response may be because the ignition advance is wound right up (for emissions, as you rightly say), slow return to idle speed is also common.
I do agree though, drive-by-wire may have some interesting characteristics - sometimes in my 156 at light throttle, 4th gear/50km/h, I get the feeling of a minute loss of power, almost as though the ECU decides the throttle's so close to being closed, it may as well shut it and cut the fuel, even if the accelerator pedal hasn't moved. I don't mind that (once I began to trust that the engine hadn't died
) as it gives best economy.
Otherwise I find the response pretty snappy when it needs to be - but a lot will depend on driving style. I tend to be a bit tolerant because the Selespeed has to find 2nd before it can really be expected to take off from a T-junction/roundabout...
On an Examiner/AlfaDiag, etc. you can see the throttle plate angle and the accelerator pedal position, so you can check they are following each other properly. Also, I cleaned my throttle body - that can make everything worse for a while, but I think it is probably a good idea long-term.
Of course, I love my 164(s), so your opening struck a chord with me
Just remember, no curtain airbags, rain-sensing wipers, stability control, InfoCentre, dual-zone a/c, HID headlights, or Bose sound system in the 164... If none of those things mean anything to you, maybe it's best to stick with the 164...