Can I improve serial data signal using reversed output on a twisted pair?
D+ and D- will be carried on a twisted pair of a CAT5 or 6 cable. As
  far as I know, this helps reducing noise and interference.


This only helps if: -


The sending end (transmitter) has a balanced (and optimally a differential) driver output
The receiving end has a balanced linear receiver that is capable of subtracting the analogue version of D+ from the analogue version of D-



  The question is: If I use the D+ line, can I do something with the D-
  line to improve the signal on the receiver?


You feed both D+ and D- into a proper balanced and differential linear amplifier and use it's output (possibly with some gain but at least one comparator), to reconstruct your digital signal: -




  The goal is the to be able a cable as long as possible (100 or 200
  meters for example) and as many nodes as possible (10, 20 etc). There
  is no requirement. Just making the best. Imagine that there can be
  several identical receivers. (not visible on the schematic) and
  several transmitters too.


In addition to what I've already said, you may need termination resistors. If I were you I'd use RS485 interface chips. They are cheap and will do what you need i.e. the important thing you haven't yet considered functionally is how to disable more than 1 transmitters so that only one is allowed to drive the line at any one time.


  So the best would be to twist the data wire with a ground wire?


See this and note the balanced drive impedances, \$R_S\$: -