So why are there no secret doors/rooms in DoomRL? That was one of the major parts of doom, finding secret areas with goodies in them. I dont think it would be that hard to implement, there are already vaults/caves generated on levels. Intuition could reveal the location of these doors. And to make it so you cant just rocket your way in, make the walls and the door in-destructable. All you would have to do is bump into the right spot the door is located so they arent impossible to get in.
Maybe also make it so no demons spawn inside them, that way if someone dosent want to take the time to track down that secret door it dosent hurt their kill count, they just miss out on the bonus items inside.