NYSE specialists/floor brokers can see hidden NYSE liquidity, though I'm not sure if they can see hidden reserves or just the displayed size. AFAIK, no one can see hidden ECN orders or ECN reserves.
I've previously said I found Open Book to be useless, so I'd say no for that. Maybe it would be helpful for thinly traded issues, but I can't say. Most platforms provide ARCA and INet as part of Lev II so you'r enot paying extra for them, and yes, I do find them useful.
Are you sure about this?floor brokers using e-quotes and d-quotes on hidden mode can be hit eletronically and according to the NYSE site can be hidden from everybody(including the specialist) The caveat is that if there is some manual trading going on he wont get anything
Yes, e-Quotes can be seen by specialists unless entered as "do not display" (but at least 1K shares have to be displayed).