As we are people who live through X set of experiences, with Y natural/biological/genetic propensities and Z set of cultural/biological/social/psychological limitations I think single most important thing a philosopher can demonstrate is that "it", that little thing that resonates with a person's identity and ideology. Not simply the "it" that says "Oh here's a kindred thinker", its that "it" that resonates in a way that forces one to think about the subject material at hand and then expand those theories and methods into other areas of life and experience. An "it' that broadens horizons . An "it" that simultaneously creates and shatters borders. An "it" that refines a process to its pure metal. Ambiguous I know but then again if Kierkegaard didn't have that "it" you wouldn't be a fan boy.

My list would look rather different from your's
1. Piecemeal philosophy, philosophy as building blocks to truth (on the fact the building blocks need to be in place before we can confirm the truth of Philosophy)
2. Truth of Philosophy
3. High Level of argumentative rigour
4. High level of rationality
5. Other: mathematical philosophy
6. Originality of thought
7. Literary ability
8. Focusing on the 'Big' Questions of life
9. Lasting Influence
10. Low Level of rationality

Of course existential philosophy has huge personal emotive importance, but I believe its a very personal and emotive field, where are different ideas are going to strike accord with different people.

This list is inclusive of a great philosopher and each trait relies on the acceptance of the prior. For example, if you do not adhere to rationality, then no matter how hard you work...It will be fruitless.

1. Adherence to Rationality - I believe that adhering to rationality will lead to truth.
2. Hard Work - The best philosophers, and the best people in any field, put in hard work. I might even go so far as to say that the best have lost the fear of hard work and rather have transformed it into something which they live and breathe--effort and the personal rewards which it brings.
3. Clarity of Writing - The more disorganized and vague the thoughts the more intelligible and useless they become.
4. Depth of Inquiry - This is a blend of rigour and creativity. The philosopher will take the extra steps to explore positions before brushing them-off or moving on; and the philosopher will make the effort to think of the interconnectedness between ideas, esp. those that he/she is endorsing.
5. Creative Abundance - The more creative the thoughts the more they will spark peoples' imagination and thinking, and the more creative thoughts that are present the more insightful the work.