I'm sure you know how the land lies with PCR, Monty, as you're knowledgable about so much else. I assume that either a) you missed the fact that these are PCR 'sister' publications or b) you were genuinely hoping to get insight from some subscribers who had found them useful in the course of their career.
My feeling is that, on the one hand, it *can* be useful in this industry to know as much information as possible, and keeping tabs on who is assigned to which projects, affiliated with which production companies etc. *can* be useful in a generic sort of way, when it comes to 'knowing the workings' of your own industry - I know that I myself frequently feel that I am not as interested or well-placed to dissect and follow the trends of the industry as are friends who work in co-ops, do secreterial work for agencies etc. So, investing in knowledge can be a good thing.
At the same time, though, there is virtually no chance, IMHO, that you would generate any actual and immediate work from subscribing to such publications. It isn't even the case that PCR only gets breakdowns after casting directors have already tried alternate routes of casting: most of its 'prestigious' listed projects have no knowledge (or interest) that PCR is namechecking them. What it is doing, whenever the famous motto 'Hold Contact Until Furthe Confirmation' is mentioned is printing something that was trawled for by 'insiders' and is being published (probably) without the production company's tacit acknowledgment, etc. These 'ads' are not adverts or requests for casting suggestions (unless otherwise stated); PCR uses them to make itself look more industry savvy, more prestigious and infulential than it actually is, and thereby defends the 'subscription' you pay for having it delivered. I don't think Mike Leigh, for example, cast his last film on the basis of applications he got from people who may have read about its early stages of development in PCR, and sent in hopeful CV's 'on spec'. Of course, there may be the odd story (amongst thousands) to refute this, but essentially, when PCR asks you to 'hold contact', it's covering its own back, and tacitly admitting it has no right to suggest that you can apply to the people in any shape, form or capacity. It knows many actors *will* do so, in the hope of landing a much - needed 'break', of course, and so simply ensures that if it gets any irate feedback from a casting director now inundated with thousands of unwanted CV's, it can always claim innocency, and point to the fact that it didn't actively encourage anyone to believe they were still casting/interested in unsolicited submissions.
I can't imagine that these publications are anything more than directories containing the same sort of information. All great if you are building a database, but highly unlikely to up your chances of securing work.