Follow up - system32\edputil.dll was what was missing for file/save dialog, "Browse for folder" tree and explorer's left pane to work properly. Interesting as this file is not present in the 32-bit image but the dialogs work properly there nonetheless.
The missing properties dialog was me forgetting to regsvr32 actxprxy.dll (whoops)
Only issue I am still getting is apps seemingly not being able to access offline registry from just the 64-bit image (double driver, runscanner, autoruns aren't playing ball). Double driver commandline for instance comes up with "Scanning registry ... Fail (a call to an OS function failed)". As ever, any help would be appreciated, but I will update again if I figure it out.
Edited by spleenharvester, 23 February 2016 - 08:01 AM.