Do bonus coin powers include territories controlled by races in decline?
No,

Each race is separate.  In this case you would not get the additional coins for forests controlled by the race in decline.

From the rules, page 5


  The Regions these In Decline tokens occupy also each contribute
  1 Victory coin to the player; Though the Race banner and Special
  Power benefits no longer contribute any bonus coins, unless
  explicitly stated otherwise in said Race or Special Power benefit.