As I said before.. I'm to LAZY to do tests, but I think that the drop in money is more about the viewers you have. Because of this, when MAX is not in a room the viewer count (and money) drops. With extra cameras the viewers are spread out and DROP in areas that Max is NOT more quickly than you gain them in the room that Max IS. Because of this you end up with fewer TOTAL viewers at the end of the day, plus I think that NO viewers get added during SLEEP.
I don't know how this might be fixed. Also, I fear that any fix could mess up the early single camera benefit. Thus I say that if someone WANTS a second camera they should put it in the POOL area. This gives the best viewer count because you can spend time with one of the ladies for a boost (Alice during the day, Lisa in the afternoon, and Kira (when she arrives) in the early morning). After the second camera choosing where to place the third (and later others) gets more tricky. I recommend the LAST cameras be placed in the BATHROOM then the PATIO(eating area). Those to seem to be the worst paying cameras (at this time). The Bedrooms don't get a lot of use right now, but hopefully will be better later in the game.
So, I recommend NOT buying cameras until you NEED them, then get the pool camera followed by ONLY the cameras for rooms that you need for events/paths/opportunities.
Hope this helps.
P.S. I ALSO recommend supporting Chocolate Chip Cookies and FIGHTING against EVIL Oatmeal Raisin Cookies.