My Philosophy Major friend resolved it well:
The contradiction is superficial, and is about the seriousness of _attitude_ with which a good artist/thinker goes about his business, not about whether Nietzsche values born geniuses over made ones.
It is not about PRODUCTION at all: "In truth, the good artist's or thinker's imagination is continually PRODUCING things good, mediocre, and bad..." That is to say, it is not the point to produce, because the PRODUCT can be good, or MEDIOCRE, or BAD, even from a GOOD thinker or artist.
It is about the seriousness of the PROCESS. It is the SERIOUSNESS of the "efficient workman's" thinking process that Nietzsche values, not his PRODUCTION. He speaks of great men having been great WORKERS, not in PRODUCTION, but in "untiring invention, rejecting, sifting, reforming, arranging." What makes a good artist or thinker is his good POWER OF JUDGMENT (please tell me Nietzsche's word here is URTEILSKRAFT). Men acquire greatness through discipline and refinement of this power, however "naturally gifted" they seem. "There is a type higher than the 'PRODUCTIVE' man," than the man who MERELY produces work.
What is vulgar? Raw or inborn talent? No. "The wish to create (i.e. PRODUCE) incessantly".
When Nietzsche talks about not having to DO anything yet DOING a great deal, it means not having to PRODUCE any WORK but yet having been a GENIUS in the thought process, the true CREATIVE process, not the jealous, envious, and ambitious need to MAKE something all the time as a showcase for vanity, or as a means of PROOF for lesser men.
WHEN the creation of the good artist finally does come about, after the seriousness and anguish of creation, then it SEEMS to others that "... their creations appear and fall from the tree on a quiet autumn evening unprecipitately [sic], in due time, not quickly pushed aside by something new."
By no means is this sort of creation spontaneous or carefree. Picasso's or Dali's work seems spontaneous and carefree to us, but could they have created it, would it have had any meaning whatsoever, without having first learned to "construct the parts properly before it ventures to fashion a great whole..."? No.