Cavity walls were done when we bought the house. Just had the loft done, free, and we are thinking of having thermostats on the upstairs rads because it's much warmer up there now.
Yes it was in our previous house and noticeably warmer.
Moved to this house with none so had it done 2 years ago. Felt the difference straight away but one draw back is if we ever any summer weather the heat doesn't get through and often feels nippy. Can't have it both ways I guess.