Depressingly little is invested in home improvements (8)
I believe the answer is:
dismally
'depressingly' is the definition.
'little is invested in home improvements' is the wordplay.
'little' becomes 'small' (synonyms).
'is invested in' means one lot of letters goes inside another.
'home improvements' becomes 'diy' (DIY is do-it-yourself work done on the home).
'small' put inside 'diy' is 'DISMALLY'.
(Other definitions for dismally that I've seen before include "How one may fail" , "Badly" , "not very well" , "lacking in cheer" , "In gloomy way" .)