I don’t think I would pay to collect air miles if their usage was likely to be up to three years away. Too much uncertainty with possible changes to the frequent flyer schemes, not least of which is devaluation of Avios and fee increase.

I do collect miles in schemes other than Avios but on the basis of them being free. I would not pay to accumulate. I have suffered devaluation with Virgin Miles which I have been collecting slowly for an ANA F redemption; there have been two during my current collection period.

The only advantage in paying to get Avios or other miles through a credit card is that it prevents their expiration if that’s part of the scheme and they count as activity. Most do. But Miles and More (LH) has a hard expiry date so even small additions will not stop them vanishing. The now gone M&M Diners Card did stop that but it was never replaced despite rumours it would be.