Well, there's a couple of issues here anyway...
Firstly, is simply time (and, apparently, the financial costs involved... RV sessions are not done on a voluntary basis... I have no ide what the money is like for an RVer, but I presume it's not $20) In relation to that, I believe that there's some sort of overlording of FS (as with many other groups), and so the projects aren't always of their own choice.
Secondly - you do realise that you are effectively asking the RVers to and watch the sacrifice - murder - and rape of children - right??? This is actually your intent!
Now, that can be alleviated by firstly doing an ARV - If X person (no, don't do groups - it makes it less accurate) has participated in Y (specific) event, then draw an apple... if they have not, then draw a pencil. That at least gives some baseline for whether to go further (for that individual and event).
I do agree about showing not only those that 'work' and those that don't. It's the same thing in the research field in general - as stated by a few of the editors (and sometimes, -in-chief) of various medical journals.. they've called for a database to be set up for *ALL* research projects, and thus for *ALL* research to get published, no matter what the results... otherwise, there's a *HUUUUGGGEEEEE* BIAS in place!
Personally, I think that RV should be used to find the *evidence* for those things that are fact... Not merely to determine whether something is actually true or not (because, many people won't accept RV alone - such as myself!)
I do agree with your thoughts about CB - he does have a knack for reading more into a session than may be warranted.