I paid 5 years NI to make up the shortfall and MrsD has just paid for 6 years (she gets her state pension next April).I'll be short too but not sure I want to spend thousands now for £25 per month later that you don't even know how long you will be around for. I think I'll be happy enough with what I'll get.
It's an absolute no brainer - you get approximately 30% return on the capital invested, and your capital back, after approximately 3 years.