I finally did get around to installing a trial of Netdrive and using it to modify some images on a remote FTP. All the images I modified got corrupted, which doesn't exactly infuse me with confidence in Netdrive. I looked at the alternatives page to which you linked, but nothing on there appears to be what I am describing.
Anybody got any other ideas? In my case I cannot use Filezilla's edit feature, because I am mostly re-exporting graphics [i]to[i] the remote site, not editing the copies that are already there.
EDIT: Not sure why I didn't think of this before, but Windows does have basic network drive mapping that is compatible with FTP. I'll try this and see how it works out.