You have certainly proposed one of the most fundamental questions of music since ever.
I have similar thoughts and questionings too, but also from a two and a half years course on Musicology I took, I can tell a few words of advice on your questions, or so I suppose.
First things first: you know "common sense"? Well, yeah, it goes a bit like that... Or maybe more than just a bit. You cannot simply teach someone how to have and think alike common sense, but you notice when someone has it and uses it in discourse, dialogue, examples, etc, as in you cannot, also, teach someone how to point out a good composition, it's more about years of experience and "awareness" than just a simple, schematic, almost algorhithmic theory put to practice.
Why is Rite of Spring valued over Firebird, you say? Well, I prefer Firebird over Rite of Spring, but I cannot lie that Rite of Spring has way more emotion flowing out of it, creative rhythms (specially for when it was composed) and has a lot more colour to it. It certainly suits a very modern ballet. For good, or bad, I stick to Firebird.
My ears tell me to stick to Firebird, my feelings to do (my brain, I could have said). It's about personal appeal, in this case, but with some "common sense" you'll notice that I admit Rite of Spring to be more original, innovative, creative and simply "better" than Firebird, despite my preference.
What determines if an idea has been adequately, properly developed? Well, to be sincere: the critics and the facts that they, one way or another, voice an opinion that lots and lots of people agree with. That is what really happens.
Maybe it's about exposition to critics's ideas? I tend to fight them off with my personal opinion, but not always, just mixing and filtering, always with some gold old common sense.
You can, obviously, listen to the masters of the past (for instance the ones mentioned for developing their ideas just fine) and search for what their developments have in common, how they worked them out and everything, I'm sure it won't be a hard task for you.
If you are stuck on deciding if something you write is good or bad, put to question two or three things: is your objective with that part of the composition being more or less clearly achieved? And: do my ears+brain comprehend what they are hearing? Is it making sense, being clear at what it states?
As pointed, there is something to do with achieving the proposed objectives: is a study hard to play and does it develop, through it's hardships, some sort of technique, more or less? Is it purely technical, or does it sound musical? Do the ideas tie together very well, or loosely?
After atonal music these questions have fallen a lot in meaning and power, but they are still valid, most atonal composers still develop ideas, tie pieces together via some devices and so on.
About the limits and horizons of what is a development and what is a new idea, I can only say that I struggle with that. It's like when listening to a contrapuntal composition, I see the commentators pointing out for the voices entering in succession with new instances of the first melody, but to me these are new melodies, for they use different tones, pitches, notes, instead of the original succession that opened the piece.
On a sidenote, people have praised Liszt for his mastery in development, while I, for instance, think he "over-develops" some of his compositions, making them boring and tiring to the ear, when they could have been summarized and made considerably less longer, more interesting, encompassing a good enough timespan of interest on the listener, once again that's just me.
Five books on theories of criticism and arts criticism it's proven to me that it is more about common sense than it seems...