In "The Ruy Lopez: A Guide for Black" the authors write about the position after the 9th move from White:
"Starting at move 9, the Closed Ruy Lopez is a dense forest of related and frequently transposing lines, mostly tested extensively at top GM level. This has to be reflected in any theoretical work - and the result will often look intimitading, with lines only starting to branch out around move 20."
What does this mean to this Forum?
1) Understanding and analysing the Closed Ruy Lopez is hard work - there is no "tic tac toe" chess, well thought evaluations are needed
2) Modern times tell people to look for simple solutions - make deviations and try to get the most of it (which means they play the Exchange or the Worrall with White or take an aggressive system (like the Open Ruy Lopez or the Arkhangelsk) as Black to escape.
3) Anyone working on the Closed Ruy Lopez has to invest a lot of time to find subtelities - just think that the Main Line Chigorin is mostly about an offside black knight (temporal advantage for White)
For myself I play the "Zaitsev" (9...Bb7) and the "Chigorin" (9...Na5) with Black at the moment, but as my white repertoire is also based on the Ruy I need to work on all lines. Consequently one can play this opening with both colours based on better understanding than the oppopent (or not of course - some painful losses have shown me).
The position after 9.h3 is complex and deep - one cannot learn every line by heart - a good mixture of understanding and knowing is the way to success (this is what Shirov tells on one of his DVDs about the Ruy Lopez).
So I really wonder how many serious Forum members are really willing to invest their time into the Ruy?