FWIW: Value of Handicap modifications seems to be dependant on several factors, the most telling of which appears to be the grace and style of the modifications...
I agree with Jim: things that scream : "Sickie/needy/health impaired" tend to take a value hit...
... and 'extreme' modifications tend to be "Cost to Remove" for readily removable unwanted features... with the typical "I don't want to have to do ANYTHING" buyer response set applying!
My other observations are that:
Wider doors work (and value) just fine as long as they don't preclude gracefull placement of furnature or function of the rooms they shelter.
Small ranch homes with extensive and/or less than graceful modifications typically take a larger value and marketing time hit than grander scale homes as a result: be careful about drawing conclusions across size/styles!
Community demographics do play a part, prowling around the census bureau data base may be in order... Some submarkets may be more greyed than others with an increased likelihood of buyer approval of certain modifications in certain areas (assuming you have sufficient sales to play with

)
Sometimes 'stature challenged individuals' value and seek HCA properties and are VERY happy with the modifications.
Interviewing some buyers and agents seems to be the best bet for finding out about such properties and their effect on value.
Sadly that takes time and energy!