That's a nice idea. I had a similar idea with card deck with "events".
Whenever the Evil player had no monsters on his turn (nothing to do) he would draw an event card, which could spawn a monster, a trap, a treasure, etc. Never finished it though, but it's on my meandering list of to do stuff :P
Your idea is great for quests that don't have many rooms or if you're playing through the quests a second time.
You could do the same with a die roll though (d20 with a list of 20 events or rooms for example)
The only difference is that a die roll may spawn the same event twice, while a card or token deck can be used for one time events of you discard the cards/tokens after use.