How does (and should) an author respond to story development suggestions

When story editing for novelists I sometimes come up with concrete suggestions for plot or character development. Faced with my suggestions my authors fall into the following general categories:

1) lalalalalalala I can't hear you
Nothing wrong with it, and I generally pick up on it quite fast. These ones often avoid reading novels in the genre that they write in for fear of being influenced. There seem to be lots of (good) reasons for this. Once I've caught on, I don't make any explicit or concrete suggestions.

2) That's an interesting suggestion.
They listen politely, but take my suggestion as an indication that something needs to be changed or added, but they will do their very best to do something other than what I suggested. I can keep suggesting things as it seems to stimulate their creativity, if only to avoid doing what I suggested.

3) Oh, wow, that would be great! Or I could...
In my opinion this is the type of response to cultivate. Not only does it make me feel worthwhile (which is nice), but I think that authors who hear other peoples' ideas and use them to develop their own ideas are the ones who remain fresh the longest. They're also the easiest to talk to. What's especially gratifying is when I suggest something to address some issue of plot or character, and in the next draft the author has created something that I would never have thought of.

4) That's what I was originally going to do, but then I thought it wouldn't work/people wouldn't believe it/it was too sad
You know who you are. I think of my job as one of serving the story, even when the author isn't. Several times in the last 12 months I've been digging around for what is wrong with a story, found what I think the story should be, told the author and had the author say "yeah, in the previous draft but one, it did that, but my mom/significant other/best mate/beta readers didn't like it". It's a bit like archaeology. I really believe that the original story, the right one, leaves enough traces behind that you can work out what it was.

5) Oh... ok.
Probably the hardest author to understand is the one who just goes away and does what you suggested. I always worry that they are being too deferential or I'm being too authoritative, and it's hard, after they've rewritten twenty-thousand words, to say to them "you didn't have to do what I suggested".

In general, an author who can pick and choose in accordance with his mood, between all of these responses, is the one who's going to improve his craft the fastest. If that is indeed your aim.

But be aware that the before the advent of the printed novel, the best stories could mature and develop through the response of the audience, each time the story was told. Each time you share your story idea with someone who isn't an author or editor, their responses and suggestions will be, and rightly, intended to push the story towards what they would like to read. Someone who is an author or editor will want to push the story towards what they think will appeal to readers, or will make a satisfying or elegant literary story, or goodness knows what else. I think that as long as you remember who you are writing for, you can make good decisions about what suggestions to take or leave, and how to communicate this to the suggester without upsetting them.