As part of Concord’s Green-Your-Heat program which ran in 2015, we got a home energy assessment and a rebate for cellulose blown into exposed, overhanging sections of the house. This has made the bedrooms more comfortable, and is saving heat.
Earlier in the decade, we installed spray foam on the roof of the attic. This has drastically reduced heat loss in the winter and heat gain in the hot summer sun. We love it. Since we implemented the roof insulation as part of a transition to electric heating, we were able to utilize a light plant rebate that helped to pay for a part of this project.
Going back further, we replaced old, inefficient windows and glass with high performance ones. The common understanding is that projects like these are usually not cost effective, but I can say it was worth it, in terms of comfort. We did not apply for rebates or other subsidies for this work. We may have gotten some tax breaks for adding foam board when we resided.
I recommend you schedule a home energy assessment to see what projects may be effective and if your home qualifies for rebates.