Well the definition of corny is :
mawkishly old-fashioned : tiresomely simple and sentimental
I guess it was at times, but not overall. They had way too much drama and bad things happening to be too corny.
I think they thought it would be funny to have a "second Nellie" but she wasn't close except in looks. Nellie was mean, lonely in many ways and spoiled rotten, made to think she was better than everyone else by her Mom. Nancy was different, she wasn't spoiled, she was just mean and lacked empathy. Without empathy, you can't feel anyone else's pain or emotions, you are void of that human part of you that make us able to work with each other and be kind.
In Tinker Jones, if she was there, she wouldn't give one toy of hers, not like Nellie and Willie and if she did, it would be something she hated and THEN she would have made it seem like she did more than anyone else. Sound a bit funny, but it's not.