There are a few other questions on this site about voluntary NICs, but these generally relate to people either retired or just about to retire.
I'm in mid-20's and, hence, immediate retirement is unlikely.
My NIC list shows 2010/11 and 11/12 to have a gap as I did not pay any NICs in those years. These would have also been before I was gainfully employed, etc, and my record since then is continuous and full (six full years right now).
Presently, (28-Sep-2018) the HMRC website shows my missing contributions to be £504.00 and £626.60 for those years. The price is said to potentially increase in the beginning of the next financial year in April although there is no scope on how much this would increase by. Lastly, it is also said on that website that my last chance to pay for these years is in 2023.
I am presently a limited company director paid through PAYE as well as dividends, but would not be surprised if I end up in a more regular state of employment in a few years' time. The only question will be whether this is in the UK with quite good odds on it rather being elsewhere (within the EEA).
Therefore, one of my potential targets could be to get the present minimum state pension record fulfilled at ten years. This would obviously be easier to do if I "bought out" those two years immediately. However, it is also possible that the minimum record for a state pension gets increased and if I only ended up with 11/12 years in total, that would be a wasted contribution I'd be putting in right now.
The above is a risk we cannot quantify as far as I can see.
However, there should be other measures that we can apply. Most people I have discussed this with (in person) have said that they will be working for the minimum (and maximum) state pension record in any case and are not particularly worried about early gaps. From my point of view, especially considering the uncertainty about future places to live in, I'm more inclined to assign more importance to these early years.
Or, lastly, it could also be possible that even with the increase after next April, I would have an easier time paying for these years in early 2022 as well as I'd have more knowledge of the situation and how it's developed up to then.
Should I pay for these years now (cheapest option), later (most information) or not at all (money could be used for other investments)?