I am a little late but have been working with YDNA results for a number of years trying to discover a break in my own brick wall. My own conclusion are that the lower marker results (anything below 35 markers) are so broad as to be only useful to saying that some other individual MAY be in the researchers DNA line but that it is so broad that much other evidence needs to be accompanied. Even the higher markers need outside evidence to correlate any matches of significance especially those other than exact.
The second part of that is the physical numbers of DNA testees within the marker levels, especially the higher numbers, to help trace the line backwards but would still then require outside corroboration and documentation.
In my own case, I was astounded by the number of "Matches, exact through 4 off" on my initial 25 marker test but after contact many of them, became extremely dishearted that we could not discover a link anywhere withing the past nine generations (I am generation six from my predecedent). after upgrading to 37 markers the results dropped drastically, only 3 exact with all of them known, but practically no correlation then between the 25 and 37 marker through 4 off that made any sense. I now have a 67 marker results and there is only one match within the family and it is within the database and there are absolutely none through seven off.Taking this a little further and comparing it to the total Y-Search database without being tied to family name only results in one line at seven off and we cannot find any connection from the early 1400's.
From my experience then, it looks as if there CAN be significant information from the results but only if there are significant testees within the higher levels to allow possible matches at no more than 2 off and anything more than that would put any possible connection probably before there were paper trails for the "common" peoples and that even paper trails for the "Elite" can be spotty at best because of the ancient policy of succeeding monarch dispatching any/all individuals in the preceding monarchy family which sometimes include their household records.