One oddity is that I have seen more than one recent substantial effort to offer help with preparation to play for the Queen's Gambit. I can not remember a recent book making a comparable effort on behalf of the Ruy Lopez. These are the two closest recent books that I can think of:
Play the Ruy Lopez by Andrew Greet (2007) https://web.archive.org/web/20140627023224/http://www.chesscafe.com/text/hansen94.pdf
The Ruy Lopez: Move by Move by Neil McDonald (2012) https://web.archive.org/web/20140627022042/http://www.chesscafe.com/text/hansen153.pdf
The October 2014 issue of Chess Life ran an article about 1 e4 c5 2 c3 .
I used to play slow d4 openings but now I will play the "best by test".