Nvm, I was at 19 for Luigi and I played one more. It is correct, you get 2 more levels. The 4th level is similar to the 2nd and the 5th level is on the roof and it is super hard for the ghost. --- http://www.section86.com/
Play 20 matches and you'll unlock two more levels. The 4th level is very similar to level 2, except there are suits of armor that rattle when players (not ghosts) get near them, and it causes nearby players' Wiimotes to vibrate uncontrollably. The 5th level is on the roof with a giant open area (no corridors, no rooms) and about 10 Monitas that indicate when the ghost is nearby by switching from a green light on their head to yellow (nearby) to red (very close). On level 5, when the lightning strikes, the location of the ghost is revealed no matter where the ghost is on the board.