I seem to be having a different experience than most of what I am reading here. I really enjoy the mansion. I find it challenging with the strick balance between speed and killing/breaking.
I solo this all the time, and have done it with groups. Groups are definitely a better way to go as there are msot spawns and thus more crests drop.
However I have only ever run this challenge once where I could not kill at least one boss.
I would say about 80% of the time I am able to kill at least 3 bosses. I average a minimum off 350 goblets (the one I run most often) and just ran one today at lunch, not opening the last two doors, or killing Rushmore and pulled in 833 goblets (on a 15th level toon running it at 17th level.)
I plan on doing a write up myself as I have grouped with enough people that have been frustrated by that that I wanted to share my experience.
The main things I do with my path that seem to be different.
Backdoor and Assassin's crib first. Open door to Boudior but do not go through. Go back through bath house to observatory. THEN to War Room and Boudiour. Back to Inner Courtyard (via back tracking or DD) then to the banner hall. I hit the SD from THIS end to kill the Mother of the Nest (never from the bath house side). And on till time runs out.
Again, this path I am 80% of the time able to kill 3 bosses and the mother of the nest. I even often avoid having the pictures spawn mobs to keep the killing down (which though may be needed for crests does slow one down). And I would have to say Soloing about 50% of the time I can open at least 13 doors. About 20% open all 16. With a party the percentages jump upwards to probably about 65% and 50%.
I have always gotten some materials from Rushmores, with the one exception. The only question I ever have about how many crests I get is how many doors I get open.