Minor idea after running into three vaults on the same level. Basically, have a option at character gen to create either the maximum number of vaults possible for a level every time, or at least one per level. Guaranteed vault generation, more or less. I guess it'd be sorta' like a spicy challenge mode, just for any difficulty level
Obviously inspired by the old ToME and its variants 'always unusual rooms' option. I always liked those for an occasional fun run.