In the version 554 there ist no Siteimport active. After installing the Programm the Field "Site import" under tools is dead. No import possible... (Tried to import a FileZilla profile).
The option is disabled when WinSCP cannot find any PuTTY/FileZilla sessions.
WinSCP looks for FileZilla sessions in C:\Users\username\AppData\Roaming\FileZilla\sitemanager.xml.
Do you have them stored elsewhere?