If you take up work immediately after retirement, at least 1 year of your class D contributions will be reclassified as A and will be reckonable for state pension.. This was mentioned at my pre-retirement course - I'll try to find a link.
Edit to add link.
https://www.gov.ie/en/publication/9...s-following-class-b-c-or-d-or-mixed-insurance
See paragraph on change of status credits.
If you qualify for treatment benefit (optical and dental) at age 66, you will retain qualification for life (under current rules).
That might be worth as much as any actual pension.