Really like the idea of possibly benevolent dwarven ghosts. If they arise from famous champions or ancestors, maybe they could even bequeath items or advice to the current generation of dwarves
Re: necro, I think a more abstract idea of 'rituals' might be appropriate.
Each civ could be given a list of events that they will celebrate, mourn, of otherwise ritualize. Each ritual would have a linked building (or buildings?) that are appropriate for the ritual in question. They would also have a profession authorized to perform the ritual - I imagine priests able to do all rituals, nobles capable of some but not others (eg: weddings?), etc.
The list of rituals would certainly include funerals, but I also see weddings, perhaps birth celebrations, the creation of artifacts, the achievement of champion status, remembrance of great victories (or defeats! - this could be either ancient history or recent), and perhaps holidays sacred for each god (corresponding to actual dates, this is a separate idea though).
Funerals would probably be the most important, though. In my scheme, a new building would be constructed, lets call it an 'altar', able to be produced like slabs are. It can be converted into one or more rooms, like chains can be. These might include 'temple', 'funeral parlor', 'Altar of joining'(for marriage), etc. Once created, the game waits for the appropriate event to occur. Then, relevant dwarves gather, celebrate, get a happy thought, and depart.
A general system like this would permit different races (or even civs...) to have different rituals, corresponding to different values, gods, etc.....