Should I be filling in "full-priced" NI gaps?

I am currently 33, including this year about to end I have 14 years of NI paid up. If all goes well, I intend to stop working at 50, which brings me to 31 years, leaving me 4 years short. I happen to have 4 years of fillable NI contributions up to April, one is cheaper at £500-ish so that's definitely getting paid, the others are full-price £824.20 each, should I be paying these too?

From what I have read, it seems like a no-brainer to do it, though of course who can predict how the rules will be changed by the time I get there. I just have to live another 3 years past the pension age and I've made my money back, and it's inflation-proof. And I get the feeling it will only get more difficult and more expensive to fill gaps in future.

Anything I'm missing or would you agree?