Fridges and freezers are among the most reliable appliances. My last fridge-freezer was about 25 years old (I left it behind, still working, when we moved), while my current fridge and freezer are over 13 years old and never had a problem. This reliability does mean that some of the older models are inefficient but still functioning well. It might be worth doing some sums on the cost/benefits of an upgrade, but don't forget that you have to pay to dispose of the old one. DO NOT do what my elderly step-mum did, and keep the old one as a near-useless sort of cupboard in the garage, filled with old plastic carrier bags which eventually biodegrade and go into holes!
It's great having self-defrosting models, but surprisingly, they don't rank in the very highest category for fuel-efficiency.