Also, I think I remember reading somewhere that Boma and Jiko did tours of the restaurants at 4pm before opening for dinner. Am I hallucinating or do they do this?
Yes, they still do this (or did in April). It's at 4 pm, and I think every day. On the list of activities, it's called something like "culinary tour" - maybe "culinary adventure tour" or "culinary discovery" or something similar.
You check in at the Jiko podium (no need to sign up beforehand - just get to Jiko a little before 4). You tour Boma first, then Jiko, and get samples of food at each.
We tried to do it in April but obviously picked the wrong day, as Boma was closed for construction, and Jiko wasn't ready for us at 4 because the tour usually starts at Boma. So, all they did was grab a server to point out a couple of hidden mickeys in Jiko, and then let us try the Taste of Africa, which is a collection of breads and dips. It was delicious, though the whole experience only took about 15 minutes because of the shortened tour, so I was kind of annoyed I had skipped a different 4 pm tour (about the hotel architecture) just for some bread and dip.

We're going to try again in October to see if we get the full-on tour! I think it would have been a blast.