I just want to say, I've read your post throughfully, from start to finish, from top to bottom, and... cake.ninjak, where have you been all my life? We're made for each other - just see the lenght of my post here. Reading through yours was a piece of cake. No pun intended.
But you see, my post, well, I was about to post something twice as big and then I decided against it, and it was going to be about what you just said - in fact, you said everything I ever believed - and, gosh, I'm jealous. How come you put it all so crystal clear? I struggle with every word! -.-
Yes, my name is Nadia and it's acceptable if you forget it lol. Feel free to call me Psycho or something. I really feel for those who want to address me but are faced with the prospect of writing my whole username... Guess that is why people remember my name. I ramble. I'll stop.
But you know, you just said so much of what I think it's almost scary. If I could add something is that, there is this thing about Background-oriented characters that are naturally tragic. Not so much by the tragedy itself, but as the way the character reacts to its past: ever present, ever haunting.
See Harry Potter as character: as an orphan, you may expect a lot of drama from him but he didn't act like the character who goes on about how he feels bad about himself and the fact that he has no parents - even if it is undoubtfully tragic.
Some may say it's a characterization flaw. But background tends to take the place of, well, that: background. So I think this was Rowling's major hit. I thought, as I read through the second book (the first book I ever read), it was actually for the greater credibility that the background did not take a major protagonism in every detail and decition with Harry Potter's life. I thought, it's true: when you are talking about your own life, you rarely see it as tragic - after all, they have to live with their reality every day.
On the other hand, past 'scars' that are worth mentioning are those more traumatic events that undelies in every of the character's most prominent traits. For example, Nadia's compulsive need to find truth and the belief that everybody is lying to her was something that came natural to her, and rarely does she remember her parents hidding from her the fact that she was a witch when she was a kid. (This is an important narcissist wound that constitutes also Nadia's first adventure.)
As for SS, I've seen people develop characters focusing on behavior more than background -- at least it's what I've seen here in the last term period. By behavior I mean, concentrating on how the character is going to react to certain stimuli. These characters are nice, very nice, and I think every character should have at least some programmed behavior in them.
The programmed behaviors can be something like this: always cranky, always smiling *cough*, always freaking out. It can be something less obvious. The behavior is the 'outline' indeed: it's there from the begining usually, if maybe by means of the 'traumas' mentioned above, but background isn't necessarily necessary. Behavior characters can be created with little to no background.
These are usually the silly characters and the ones who will always react the same to almost everything going on, and make good fanfiction as well as comedy character. (However, strong behavioral characters are a bit dull unless you can always find a way to pour your creativity in each response.)
AND yet there's another option, of my preference, and I call this RP-oriented attitude "player's performance". NadiaIC was a player's performance character, which means a character that adapts to the creativity of the player -- in other words, the character was open-ended enough for me to chose the reaction according to what I find more entertaining.
It can very well be described as whimsical
That's its best virtue. And I think this is the character type you were trying to describe in your post, cake.ninjak? In this type, the credibility relies in a number of things, most of which you already described in your post.
Heh. I realize I ramble but maybe somebody will find this information intresting in some way. It is really an extension of my previous post: the credibility of the RP can be achieved with no problem despite the clashing of background (which can be dealt with by either compromising or ignoring each other), but you can also very well make characters whose background is not such a major part of the character composition and still be credible and entertaining. Er, sorry if I made it a bit long and confusing.