My first games hardly ever had a chance to reach the better 2nd level, but I found the mixing levels option far too random. Having played a bit more now with different players, I have found more strategies in getting to the 2nd level and, more importantly, still getting out again. I had already sussed out the links from the Secret Room, but have now found a risky way to attempt the 2nd level. Using the 'Blackmail' card is instant exit, but you have to gain at least 4 DF first to compensate for the loss of 4 random DF.
The more I play, the more I discern about the game which seems so simple and straightforward at first glance. I still think it cries out for expansions and that the 'different operatives' was a missed opportunity - see other topic - but I have to admit that there is more to this game than first appears. Cheers!