The evolution of features of writing and writing systems are not unidirectional as Tim Bulkely comments,
The changes in chunking and in extra textual cues have not at all been unidirectional, and are fascinating to track.In order to provide some context for Tim's remark, I offer these two images. The first is the Cuthbert Gospel, more information here, a 7th century Latin text in the style of the Lindisfarne Gospels. In this Latin text, there are word spaces as well as line spacing which reflects phrasing in the text.
The second is the Khitrovo Gospel, 14th century. In this text, there are no word breaks although there are punctuation marks and other diacritics. It is evident, however, that the lack of word spacing does not reflect a need to conserve paper. It is difficult to draw conclusions about the function of literacy in a society by the presence or absence of word spacing. However, it is safe to assume that as a particular style developed, it became an identifying feature of writing for that culture or subculture.
Note. I had orginally found this image of the Khitrovo Gospel on this site. However, it is no longer there, but I have retained a copy of this image since 2005.