I can usually find only 2 of any of her given books in a store at a time. I would recommend trying Amazon though. I would also check some used book stores. I have one here where I found Water Witch (I was very excited).
I would completely recommend Miracle, I read it every year around Christmas time and I love it (and I'm not very into the holidays). It also has a TON of recommendations of other books to read (and movies to watch!).
Remake is a good quick read, I think Lincoln's Dreams was the hardest for me to get through of her stuff (even though I still enjoyed it).
As for type, I'm not sure really. I bet you have a point here. I think Passage (for one) really could have been classed as popular fiction, I have read other books in that category that are no less fantastic. Most of her stuff is not what one would normally think of when they hear the words Sci Fi Lit.
I made a friend of mine read it and she is not at all into Sci Fi but she loved it. Most of Connie's stuff does probably appeal to a slightly different audience but she earned her stripes with Sci Fi (at one time she was the only femaile to win every single Sci Fi award, not sure if that is still true though) so _she_ is probably the one who allies herself with that genre.