The discussion seems to drift from the Imagerie card mechanic towards the practical implications of illusions. I'd suggest a different discussion (sub-)thread for the illusion mechanic. The card in itself produces creatures, an ability already worthy of discussion.
(I hope I don't bypass a lot of discussion; I read all the forum guidelines, but I might miss some discussions that cover exactly that what I suggest. However, in this case the discussion seems diverted)
On the card: For such a strong mechanic I especially like the non-altered CC and activation cost for the upgraded card for symmetry reasons; on the other hand, somehow I feel this might be slightly overpowered for the upgraded version.
For balance reason perhaps this card could be split in two cards (four versions): permanent with activation cost (plus upgraded version) and a spell variant (plus upgraded version).
Also, there might even be a distinction between cards that produce illusions and cards that don't. It makes better use of the design space as I see it.
To conclude, I definitely like this card 8)
