I think there is a difference between naming rights and title rights. The former will enable the rights holder to name the stadium completely after a brand name like the Emirates Stadium, the Etihad and the Allianz Arena etc. without a trace of anything else, which tends to pay a lot more. Some US venues have been able to get more than 20m a year for the naming rights. Title rights, the way I understand it, is basically just adding the brand name to the stadium's current name, without wiping it out clean completely, for example Spotify's deal with us right now. Therefore it generally bring in less money than naming rights.
However, I think once the Nou Camp Nou is built, we are trying to sell either the title rights or naming rights for a lot more money, I am hoping it is the former as we should always keep "Camp Nou" as part of the name. Also, selling naming rights is confusing and might hurt the club, for example, imagine if one day Allianz stopped sponsoring Bayern and sold its shares they have in that club and completely withdrew from that club (very unlikely, just hypothetically speaking), and somebody else bought the naming rights, Allianz Arena will be renamed as "Blah blah blah Arena" all of sudden, it is just odd.