The tutors you mention here all have an condition, the majority require a deck to support them and they are quite expensive provision wise.To my view, cards like Oneiromancy — at any price — are bad for the game. And comparing them to any of the myriad of other unhealthy tutors (Royal Decree, Land of a Thousand Fables, Geralt Quen, Call of the Forest, Avallac’h Sage, Amphibious Assault, Blood Eagle, Roderick of Dun Tynne, Whispering Hillock, John Natalis, Ermion, Ge’els, Menno Coehoorn, Vabjorn, Whisperess: Tribute, Fauve, Ferko the Sculptor) is not meaningful.
Oneiromancy doesn't have any of these downsides except it has higher provision costs BUT due to echo effect this doesn't matter.
In the posts above I see a lot discussion about rating the cards value in points in all sorts of complex ways.
You've got to rate this card in provisions Oneirmancy is worth 20 when you compare it to similar tutors:
Royal degree for an unit
Land of thousand fables for a spell
Avalach sage for an artifact