Here's something Impressions dude Lancer27 wrote a while back, I hope this helps. -------------------
Your housing needs a variety of entertainment and there is also a boost for city wide levels of entertainment (as reported on the Entertainment advisors panel).
Here's how it works: Each house has an entertainment rating on a scale of 0-100, the level is based on the walkers that pass by and the city wide coverage levels. So, you get some point if a theater walker has passed by. You get points if an amphitheater walker passes by, and more points if the amphitheater is hosting 2 types of shows. Ditto for Coliseums. You get points if a Hippodrome charioteer passes by. As you'd think, you get more points for the more expensive structures than the cheaper ones, with a good boost to Amphitheaters/Coliseums if they have two shows. These points add up to a total of 80, maximum.
How recently a walker passes DOES have an effect, the points tick down with time: you can see it graphically by the height of the overlay columns which decrease with time after a walker passes and eventually go away if no additional walkers come by.
The other 20 potential points comes from the city-wide coverage level of the various building types. So, if you have perfect (100%) coverage of three types of entertainment, but no Hippodrome at all, you would get 15 of the 20 possible bonus points in every house on the map. This can result in houses that have no entertainment walkers passing at all having a high enough entertainment level to make it to the small/large casa level (which require 10 points of entertainment).
I find this added bonus quite useful if an area with plenty of theater/amphitheater walkers is not evolving to a uniform level of insulae: building a Coliseum or two, or a Hippodrome (1 hippodrome gives perfect coverage, so its a quick 5 pt boost to every house in the city, even without walker coverage) will give enough of a boost to get some more housing evolution in unexpected places. Neat, huh?