Yes, apart from cache (which I somehow managed to NOT clean for almost a year now - which is convenient, as this stores all the login data for services), you can safely delete the contents of the following directories, some of which are constantly growing:
WARNING - this will also clean the queue and the download history!
(which may be a good thing)
SF_TMP\outputTemp
SF_TMP\picture
SF_TMP\MetaPicture
SF_APPDATA\localdata
SF_APPDATA\taskdata
where
SF_TMP = General -> Temp Directory>
SF_APPDATA = \AppData\Roaming\DVDFab\StreamF ab>
Obviously,
you need to close SF before doing any of this.