Though put to Alan (#13), I think the random/speciicality issue probably involved a mix of factors.  Almost without exception faith in him as a thaumaturge was present.  When he healed many (not all) we do not know whether 1) he simply tied and needed rest, 2) some lacked faith in him, or 3# whether the day’s preach had been done.  Theologically 2) & 3) would be similar, prophetic of the fact that redemptively not all would be redeemed – redemption is one meaning of the word translated ‘heal’.  That in turn is linked to individual faith.
  I hold that to signify his messiahship, as well as to highlight his deeper level service of redemption, Jesus came with significant yet limited physical healing – hence John’s use of sēmeion.  Likewise the earliest apostles had this supporting feature.  Occasionally Jesus selected an individual to heal (eg Jhn.9), even as he had selected a few to be indepth disciples.  Likewise John & Peter (Ac.3:6).
  When it’s taught that miraculous physical healing happens, faith levels rise enabling a greater uptake.  In some countries this combines with a ‘time of visitation’, miracles supporting the greater miracle of redemption (Jhn.14:12).  Missionaries, whether apostolic or not, sometimes exercise more faith in W3 countries commensurate with the community belief there.
  One issue with #21 is that the ear was not created de nova, but was simply picked up and miraculously sewn on – perhaps restoration rather than regrowth.  Thus it does not exemplify #1’s line about “regrowing lost body parts”, a line I have taken to quality the Q.  Personally I do not have a problem with extra-ordinary miracles in this life including regrowth of limbs, eyes, etc.  It is more a case of being in God’s will for the given individual.  The resurrection will involve redeemed spirits summoning back atoms for at least the basic human frame, though I suspect that even functions like taste buds will be included – eating for pleasure, not sustenance.  To some extent regrowth in this life hints at the greater miracle to come.