We currently have limited resources to dedicate to 'cluttering' the world. We have need to create these small caves and tombs that aren't necessarily associated with any quests. I suggest we have a 'generic interior' designed for each type of these, with limited clutter and spawns. Fully nav-mesh these things, and just copy/paste them as placeholders for these tombs and caves.
Likewise, the same could be done for new NPC housing. The idea is to give all the NPCs in cities a schedule, so they seem dynamic. At the least this means they should go home and bed at night, and wherever they're normally found in the day. Morrowind was not built to have a bed for every NPC, like Oblivion and Skyrim. There are many many NPCs that don't have beds. To fix this, we could do one of the following, or a combination of them:
1.) New houses of a particular style with an accompanying 'generic interior'. Hlaalu building style in Balmora and Suran, a Redoran one for Ald'Ruhn and Gnisis, whatever. These interiors would include a bed (marked for use by whatever NPC), and very basic furniture. That's all. No clutter, no unique touches. Copy paste all new player housing for a particular exterior to use the cookie-cutter place holder. In time, people may go through and fill out the character of these abodes by shuffling the furniture, adding clutter, whatever.
2.) More beds added to 'taverns'. Places that rent beds could be greatly expended to handle the population of towns. Guard posts could have extra 'floors' dedicated to loadsabeds. (this would work especially well for the characters without homes who are already in those taverns)
3.) Tenement housing. Make large apartment styled buildings to places with high populations and limited space to handle NPCs. Rooms for these buildings would follow the same limited cookie cutter layout of houses. Some of these might even lack proper interiors and be open shacks with nothing more than a bed and a random container loot chest. (this might work for the shantytown shacks planned for Vivec).
4.) For the homeless NPCs, maybe have floor mats in alleyways they will use to sleep. Or perhaps they will be offered beds at the temple. Or for large cities we could dedicate buildings as homeless shelters with several free beds. (if the player uses these there could be a not-negligible chance at catching a disease or getting an 'unrested' message).
Point is, if we can get a volunteer to make these 'place holders' (shouldn't be hard, as the cluttering for each of these would be minimal), we can go ahead and include all the generic caves, and ensure everyone in a town may have a proper schedule without worrying about clutterer resources. This will allow us to better plan out our cities once all the interior model resources are made available to us.

Something else to consider,
Something else to consider, there doesn't seem to be a list of caves and tombs that are not quest-related. Thus, over the next few days I'll be posting in this thread a comprehensive list of locations that are not affiliated with quests. We can use this to at least see what all needs to be done. Some of these locations are already completed, so we'll have to create a project list if it's not already completed.
EDIT: There is already a list with a link below, courtesy of altea.