Hi PEI_3727,
Your reference to SAE recommendations is interesting, but I'm afraid your being "unfamiliar with the particular equipment" shows clearly when you go on to remark that:
"[...] but this should not be at the expense of introducing another error: – reaching for the selector knob without looking and choosing an incorrect control; or looking at the selector then back to the PFD with associated increased workload."
So let me explain the situation from basic principles (A320/330/340/380 pilots can go off and make a cup of tea, and/or concentrate on the Six Nations rugby match).
When the AP is engaged, the PF makes his/her own altitude selections using the selector knob on the FCU. (S)He must monitor the flight-path on the PFD and ND (nav display), and - in climb or descent - needs to minimise the amount of time looking at other parts of the cockpit. The PNF monitors the selections made by the PF, and - when they have been completed - calls the associated FMA changes (i.e., any required by company SOPs) as seen on his/her PFD.
So: back to the selection itself, in this case an altitude or flight-level change. The PF switches his gaze from the PFD up and across to the FCU, and reaches for what he thinks is the altitude selector knob. Touching the knob but not yet moving it, he averts his gaze back to the PFD. The values of the 4 parameters that can be adjusted by the 4 FCU knobs - SPD/MACH, HDG/TRK, ALT, and VS/FPA - are all visible on the PFD in one form or another.
The PF turns the altitude knob, simultaneously observing the changing value of selected altitude or FL. If he is turning the wrong knob, this will be apparent immediately. (The easiest pair of parameters to mis-identify on the FCU itself are the adjacent SPD and HDG knobs, whose associated read-out windows both show three-digit values. On the PFD, the parameters cannot be confused.)
Finally, the PF pushes or pulls the knob, depending on what type of climb or descent he wants (or leaves it alone if he wants to use VS or FPA). Now for the crucial bit. The PF continues to watch the selected altitude until his hand is well clear of the selector knob, to ensure that he has not inadvertently turned it. The PNF can now announce the FMA visible on his PFD, e.,g.: "Open-descent flight-level two-four-zero."
When the PF is hand-flying, the selection roles are reversed, except that, if the FD is being used, the PF first has to tell the PNF what (s)he wants; e.g., (s)he might want a change from managed-descent to open-descent, or even VS or FPA. That increases the workload for both pilots.
To sum-up, PEI_3727, there is no harm in choosing the wrong knob, provided you don't turn it until you are watching its effects on the PFD. And the less time your eyes are away from the PFD, the less likely you are to deviate from the intended flight parameters.