The side effect of that change is that I can have two wandering monster tables, one for when I roll a 5, the other when rolling a 6. The first table would be the level-specific or area-specific table; the second would be dungeon-specific or specific to a larger region, with a couple entries pointing to an "anything goes" table to represent new arrivals from completely outside the area.
Another change I've been thinking of relates to frequency of rolls. Once every other turn is the default, but making a loud noise sparks another roll, while taking measures to reduce detectability decreases the number of rolls per hour. There are basically three methods of attracting attention in the dungeon: sound, light, and odor. Countermeasures against each, listed below, eliminate one roll per hour, or skips one hour of checks if you go below 1 roll per hour.
- Sound: Avoiding any conversation and wearing leather or no armor. One person traveling alone counts as a separate counter measure.
- Light: Traveling an entire hour without light counts as one countermeasure for just that hour. There's an immediate check if you suddenly use illumination (brief uses of a shuttered lantern, for example.)
- Odor: Masking odor, in a dungeon with animal or bestial inhabitants, counts as one countermeasure. If there are several wandering creatures in the area that don't use the sense of smell, masking odor has no effect.
Also, using the Silence spell halves the number of checks, instead of dropping one check.