Ok, I get the basic steps:
1. Have a Sim die while there is at least one other living Sim on the lot.
In my experience, this is not
necc for two reasons.
1. With a lucky roll, I guess, I've had a sim get that opportunity after relatively shortly after befriending and romancing up a pre-dead ghost. However, trying the other way has actually taken me forever and a half. I have some saves I've given up on for just the same problem you mention.
2. Curiousity got the better of me, so I put on my
robe and wizard hat lab coat and ether goggles. I was specifically testing if you can get the "manage the dead" masoleum option to grab the grave of a sim that died while living alone -- provided you load up the lot of someone s/he befriended. After maxing CASsie's friendship with Leighton, I had her starve in the park. (Three times, before I removed the unlucky trait. Before then, I thought "lulz!pity" from the Grim Reaper was an
occasional occurrence with that perk. Er... what are the actual stats?) Loaded Leighton, and no option appeared. Hrm. Checked the park. The grave was still there, and he could pick it up. Whoohoo!
Then I got curious again. This time, CASper died
inside his trailer, with new bestest friends in the Bachelor house. Again, no Manage The Dead. New CASper moved in, and lo and behold. Grave. Not where I left it, but still in the house. Killed him, and moved someone else in. Got the burial ground event, and went with it, for fear of wiping the other graves along with the new ones. Original graves still there, with collectable gems spawned on them like the others.
So it seems character death isn't really all that permanent. With some patience, luck, and ambrosia, it might be possible to have them up and breathing again. I think. I haven't really tried yet.
... Which is completely irrelevant in and of itself to what you said, but here's the relevant part:
What appears to be the deciding factor is your relationship level with the ghost. Since the graves aren't destroyed, even if they die alone at home, you
can gain access to the ghost, and build up said relationship. I'm not recommending planning it out that way, since it could be more trouble than it's worth, but it still allows for flexibility if this is something you want to push later on in your town. Or, if your sim
actually dies accidentally. It happens, right?
What is it that makes the playable ghosts especially boring? Can't they do the same things as every other sim?
That's what makes them boring. They're pretty much just see-through Sims, with no neat, ghostly quirks. Fine as Sims, boring as ghosts.
It kind of bothers me how ineffectual they are in comparison to sims 2 ghosts, but they are purty. Also, ghost babies/toddlers don't earn my hatred nearly as fast as their living, and gratingly louder, siblings.
I was disappointed to learn that they aged. Seriously? I understand that it probably keeps the ghost babies from being forever so, but... I feel like there's gotta be something else that can be checked against.
[Edit: alone, not along. Though the idea of a die-along is kind of amusing.]
[Edit 2: Gah! Double post fixed. Sorry.]