Among the names you mentioned, I think only Gortat could still potentially benefit us with the minus of Neal. Not all the rest are scrubs as Millsap surely has values, but they cannot help Spurs more than Neal.
On the other hand, although he is very important to what Spurs are doing now, unlike Leonard, Neal is not your legit starting SG. So for a tanking team, why do they want Neal for their future? I'm not saying they don't want Neal, but they definitely don't give up Gortat or Millsap to the Spurs with Neal as the centerpiece of the trade. You need to give up Leonard and draft pick, etc.
Then hypothetically, even if Spurs is willing to give up Leonard for Gortat, they sure don't want to add Neal into the package. They will only insert Mills/Blair/Bonner if the other team asks, but not Neal. So we are back to square one, it's hard to trade Neal --- as the centerpiece --- to get a more valuable player back.