Thanks for the answers.
IMHO, I don't think the Day/Night card is rubbish, on the contrary! I think that it's one of the great ideas in your expansion, which brings something new to the game. One way to avoid strange texts on the cards like the one I mentionned above, would be to make the use of the Guardian and the Herald mandatory (as I thought it was). All the elements of the expansion should be used. I think that the size of your extension, comparable to the size of CotDP or KiY, means that to make it interesting, and meaningfull, you need to play with the entire expansion... (I always play with the entire CotDP)
Anyway, please don't throw this Day/Night card away, it's REALLY great!!