Just speaking for myself, if I went to a site, was able to create a reading list, and then had to do it again the next time I went, I would probably be too frustrated to return, even if I later got an invite code.

Also, someone who comes to the site without already having a list of people in mind to watch will probably just want to use the random user / random community / latest things link from the logged-out homepage, and might be confused by being asked to "make a reading list now", especially since those settings would only be saved in a cookie. And someone who gets directed to the site by a friend ("here's a link to my Dreamwidth journal") is likely to be able to ask for an invite code from that friend (or already has one from that friend.)