My wife and I were in a similar situation with the opportunity to buy into her pension plan at an international organization (like the World Bank) for the 3 years that she was on leave without pay before resigning. Each year would cost us about 8% of her annual salary to increase her pension by 3% of her high two years working with the pension fully COLed (including while it was pending!). Virtually a no brainer! But I would still be careful about committing too high a proportion of my resources to something like this.