I didn't upgrade anything during the 1st generation. The reason for this is that by the time they had the money, they had already naturally made it to level 6-7. No point. What if the 2nd gen uses a different area? So, I upgraded the area as soon as I got my 2nd gen person and knew what area would be used.

I don't spend money if I can help it. The interest is what makes it add up fast!