I've just found this site.

http://abc2xml.appspot.com/

It converts ABC to MusicXML. The saved results can be opened in Musescore. It's all pretty painless as a process, but a bit long winded. I suppose the editing has to be correct in the first place and an online forum suggests it will only do one file at a time, not a song book. I've not found an equivalent for xml2abc.py.