When you select an Array element (the line with the blue number), did you ever notice the little checkbox in the Options Bar?

By toggling this value, you can tell Revit to either add extra elements between the first and last element (thus squashing the elements closer together), or append elements to the end of the array using the current spacing.

Heads-up for this great little tip goes to Revit Family Planner:
Die Optionsleiste oder Neues (?) beim Reihe-Befehl

Do this:

  1. Place a new Room
  2. While placing, adjust the Limit Offset in the Properties Palette.  Everything is ok.
  3. Now, still while placing, adjust the Offset in the Options Bar.
  4. The Properties Palette is grayed out!  Looks like the Options Bar is top of the food chain…

“Changes made in the Option Bar super cede the newer data entry capability of the properties palette”
Properties Palette VS Option Bar – IMAGINiT Building Solutions Blog