Is this a reason not to max NI contributions

At retirement I would expect to have a full state pension and my wife to receive the IQA.
Her only other income would be from UK state pension which we are currently buying back years.

Of course these figures will shift over time but I'm just looking at it in todays money and since the IQA starts to taper out at income over €100, is there any point in her buying back years that would generate a UK pension of more than €100/wk?

A very interesting question.

If she is buying at Class 2, the return is so great, that buying back, if it is wrong, would not be wrong by much.

And the rules or your circumstances could change, so having an independent source of income could well be right by a huge amount.

If it's Class 3, the decision would be much closer.

Yeah she is class 3.

Just checking and the IQA cut off has only moved very little over time.

Weekly Income Floor and Ceiling for a Qualified Adult (1992-2023) source

So I think we might just bring her to 10 years contributions to claim minimum and revisit a year or two before retirement to see if it is worth buying extra years at that time.