The "long" is needed twice. There are "long silk stockings" and there is also "long flowing hair". Omitting either "long" would allow short(er) stockings or short(er) hair to be considered. (Side note: the phrase "flowing hair" does not seem correct to me. I would expect it to always be used as "long flowing" when describing hair.)
I regard all the commas in the quoted text as "listing commas". They whole quote says that Widle has five relevant attributes
- flamboyant personality
- wearing long silk stockings
- long flowing hair which gave the impression of a general air of wittiness
Each comma could be replaced by "and" but that would make the sentance seem clumsy and it would be an unusual way of writing such a list.
Your comment asking about replacing the comma before "long flowing" with "and" made me reexamine the whole quote. The words "which gave the impression of" might be joining two aspects of the writing. First that Wilde had three visible attributes and that they gave the impression that he had three qualities. I believe the sentance could be split into two, as follows:
On his arrival in America, Wilde stirred the nation with his
flamboyant personality, wearing long silk stockings and long flowing
hair. These things gave the impression that he had a general
air of wittiness, sophistication and eccentricity.
With this two sentence interpretation it would be correct to replace the one comma with "and", as done above.
If the one sentence version saying Widle has five attributes is correct then replacing the comma produces the phrase "wearing long silk stockings and long flowing hair" as an item in the middle of a list. This form suggests that "wearing" applies to both the stockings and the hair. People do not not "wear" their hair, unless it is a wig, so the the phrase seems poor to me.
When I write, I try and avoid using "and" in the middle of lists as it often leads to difficulty in understanding what is intended.