I don't think we need Felica-Day-level actors and actresses, though they do add alot of flare, its enough that they have Alot of people so that everyone doesn't sound like the same person. New Vegas did phenominal with this, I hope they continue the trend.
Turning this thread on it's head, another thing I would like to see regarding celebrities are more In-Game gossip, grafitti, posts and even statues being made about in-game celebrities. I think there would be Much more gossip and such about the rulers of a particular town (especially inside that town), and all sorts of senseless, arrogant notices and "advice" from ruling families around - as well as some not-so-nice grafitti on walls in the lower districts of the city that chastise them. I imagine it would add more spice to the game, a bit more realism to the nature of big cities and much more immersion.
I felt New Vegas did a better job of adding grafitti to walls, much moreso than we saw in Fallout 3 or Oblivion. I would Love to see about 10 times more of that in the spirit of the day (rants about the king!).