Slight necro up there, but this is one of my favorite topics, so I thought I would comment, too. I personally prefer the method of keeping 2 main rngs. The first would be for level generation, the second for everything else.
With Strife(which I am planning to get back into), I have a basic world structure that gets generated upon starting a new game... an overworld
is generated by randomly choosing n spots across the map, where n is a random number inside a certain set of bounds, and is chosen as the first thing after the map seed is set. These represent seeds of random terrain features called regions(mountain, lake, plain, forest, desert, swamp, volcano) which are chosen using weights to create an acceptable distribution. (E.g. less volcanoes, more plains) All the map cells are assigned to a region using a voronoi diagram approach.
At this point, I generate the dungeon seeds for all mountain ranges and volcanoes, which are placed in the geometric center of the region. This includes how deep they go and difficulty of the dungeon (chosen based on the starting location of the player), any special rewards, and the seeds for each level. I also generate city seeds for all the regions that were determined to be "bountiful" enough to support a city/town population.
Because I have the ability to generate the level from a seed number, I can easily store level deltas... changed doors, smashed walls... etc. while maintaining a smaller memory footprint. Items, traps and monsters are spawned outside of the seed rng (and consequently have to be saved as additional info about the level), but could easily be worked into the process if you wanted the monsters and items to be the exact same each time you chose a specific level seed. (which I chose not to do)
This allows the ability to play in a familiar world when using the same seed, but make sure that a player can't gain a substantial bonus through brute-forcing the locations of desirable items or artifacts. Anyways, that is the balance that I decided was fair for my game. It will be different for everyone.
I would also like to mention how useful this feature is while developing. I can just manually set the world seed, which allows me to test in the same environment every time... If I encounter an error with map generation, I know exactly how to reproduce it, and i don't have to generate any previous maps before I can get the RNG back into the state that generated the troubled map.