Didn't Jesus return to Earth after the resurrection when he appeared to Paul? Why has anyone not brought to light Jesus return to earth when he appeared to Paul while Paul was on the road to Damascus? Was this not a return of Christ when he called Paul into the ministry of faith?
I think you might be overthinking this. Going by NKJV, Acts 9:1-9, Christ did not necessarily "appear" physically. Verses 3-4 only indicate that Paul heard a voice and saw a light, and that light could have been anything


  As he journeyed he came near Damascus, and suddenly a light shone around him from heaven. 4 Then he fell to the ground, and heard a voice saying to him, “Saul, Saul, why are you persecuting Me?”


That's not really much to go by, and that brings me to my second point: if this was the second coming, why would Paul not write more about it? Typically, when something in the Bible (or really any other documentary) is important in some way, there will be more than a few sentences explaining the importance. 
That's not to say this event wasn't important; it is, but for a different reason, and as a matter of fact this importance is elaborated on (at least, more so than anything about the encounter with Christ itself). If we look later in the chapter, we find a part where God explains to Ananias the significance of Paul and why he needs to be healed.


  13 Then Ananias answered, “Lord, I have heard from many about this man, how much [b]harm he has done to Your saints in Jerusalem. 14 And here he has authority from the chief priests to bind all who call on Your name.”
  15 But the Lord said to him, “Go, for he is a chosen vessel of Mine to bear My name before Gentiles, kings, and the children[c] of Israel. 16 For I will show him how many things he must suffer for My name’s sake.”


This is the significance of the event: not that Christ appeared (as he has many times to many people since then), but that his appearance changed someone's life and turned them into one of the Lord's most influential followers, if not the most influential.