Our local code allows 9 circuits on a 20 amp breaker. I see where on alot of trac homes the contractors install a 12 space panel for an entire 160 sq ft house. This usually includes heater and A/C with electric water heater. We do not do trac homes. We do the smaller type home that usually starts like a trac but is sold before it is finished. Instead of trying to see how cheap we can be we try to wire the house as if we were moving into it. I found out that most people don't mind paying a little more if they are getting a better job.
Around here the average home goes for $125,000. So if the electrical is $1200 to $1500 more just because we used a 40 space panel, spilt the circuits up so there would be no nusiance tripping, installed just a size larger wire to the A/C unit so the lights would not dim when it started. The builders just add it into the price and the homeowner is satisfied with the product.