I think the answer to this question will very for everyone. Also, as we learn more about music, one's idea of musicality will evolve and grow to become more effective.
Rather than invalidating our earlier views though, I think our ideas can just become more complex. From the point of view of the musician, if I can take an earlier simple piece that I learned and apply those ideas to a new piece, that application provides a new musical ideas. If I just learned to apply a crescendo to a phrase while practicing Fur Elise for example, I now can find places in each subsequent piece I learn where I can apply a crescendo. In doing this, I may find places where I feel a crescendo is shouldn't be used. With this, I may rethink my placement of crescendos in the first piece improving it's musicality. However practical or linear as that may seem, it's not that easy. Even just phrasing and placing a crescendo in thu examples is complicated and that takes a lot of reading, learning from our teachers, listening, studying the music, etc. We also must manage and balance many of these elements at once to create our overall musicality.
For composition, I think the composers ability to express their ideas is what makes something musical. They do this in the context of a form, key, constraints of the instrument, and any number of other elements. For some works, a composer may make something incredibly obviously deep and musical. Some may feel that a minor key and deep lyricism makes a piece musicality, others love strict counterpoint, some composers found shaping their music into a form helped them express their ideas. In some periods of history, freedom from form was an innovation. It's something incredibly difficult to place in a general sense.
To say that all compositions must comply to a single view, would severely limit my views I think. So instead, rather than defining my musicality and then finding compositions that fit a single view, I think it's much simpler to look at a piece and ask myself why it is or isn't musical. I think it's in part because I'm an art major and we're taught this method of critiquing art; the method has us (1) look at what the work of art is of in nonobjective terms--if it's a red line, then say it's a red line and not what that line may represent, (2) point out each of the basic elements the artist used--such as a strong sense of color, (3) see what the message of the work--this part is up to interpretation (4) look at the emotional impact of the work and finally (5) decide whether we like it using these elements to discuss the opinion.
Even critiquing the same work of art, different people will come with different opinions as they'll note different elements. For example, some people may find emotional impact is important while others may appreciate the use of contrast. In the case of art, both appreciating the use of constrast and emotional impact is artistic; for music, effective use of various elements would still be musical. This is similar to the earlier example in that as one's understanding elements grows, they may appreciate a work differently. Certain elements in a piece that you used to appreciate, you might later decide you no longer like. In a piece you once loved, the harmony may now seem bland. You might not have noticed something's in a piece you used to hate that now makes you love it.
These are just some thoughts. I'm sure other people here will have good ideas on what is musical that I'll agree with and add to my understanding. My understanding of musicality will hopefully continue to grow for life. Should I ever insanely come to the conclusion that my musical growth has reached the ultimate level possible, I'll still hopefully continue to search and somewhere there will be a new idea or point of view I couldn't have considered. It's impossible for any individual to experience everything; even everything within the scope of music would be incredibly difficult. Reading about Beethoven or even the great pianists of today, they always continued to innovate and create new things. With each composition they wrote or piece they played, they learned something. I think to say that one person understands or defines all that is musical would be like that person claiming they were better than Beethoven and all other greats. That would be a bit off, imo.
Topic: How do you define Musical?