Replace an older anything for that matter. All about energy preservation as you stated.If you have an older fridge, look into whether your local utility company pays you money to haul away your old fridge and gives a rebate if you purchase an energy star certified fridge.
If so, this would be the best time to replace the fridge.
Also, for AC units, the higher the BTU's, the lower the bill.....because it doesn't have to work as hard and isn't clashing with the existing heat.
Folks would purchase a 5,000 BTU unit and put it in their living room 'cause they're too cheap.....though it ends up costing them more in the long run.