Just going to put my two bits in: MN could either do really well or really crappy in theaters. On one hand, if they market it as the prequel to LWW and emphasize that connection, it would probably draw back a few people that we've lost along the way. On the other hand, the creation aspect of MN would probably drive away the non-Christian audiences of the casual movie-goer audience. But if they try to water down the creation aspect of MN, they would alienate pretty much everyone else. I think it could go either way though.
As for doing SC next, it would all depend on Will Poulter, now that the last of the Pevensies are gone. But honestly, his portrayal of Eustace is my favorite part of VDT. He perfect. I know of so many people who were overall disappointed with the movie but loved Eustace. If WP isn't in SC if and when it gets made, I will probably cry.
And on a random note? I doubt the screenwriters can do a worse job than those who did the Eragon movie, so I'm not concerned about the worst book-to-film adaption, because I've already seen it.