I'm sure I'm not the only one who have my sims only dedicate themselves to work and skill building, always trying to get to the top of their careers. If you play this way, yes, money is going to come easy.
I've been trying to make my sims more social, have them visit other lots, and try to make them less "skill build happy" to slow career progress. Sometimes I will purposely not raise a skill so they don't get promoted. Switching/quitting jobs help too. Move to a bigger, more expensive lot that you have to redecorate/upgrade. Donate to charity a couple times a day. Hire every service and don't have either the frugal or free services rewards.
I had downloaded an updated version of Judith Ward's lot, and her bills were a whopping 27,000 simoleans for the week. That and I've noticed that the bills are much higher in the game thanks to the thermostat that came with Seasons. I've even had to move some sims to apartments because their weekly bills would leave them only with a few hundred simoleans left, especially if I had only one sim in the household working and had the thermostat on when it was super hot or cold.
I agree painting and writing have problems. They finish paintings in only a few sim hours and my sims write an entire novel in one day! For this reason, I have both the slower painting and a slower writing mods (I think it doubles or triples the normal time) so it seems so much more realistic and helps with the ridiculously fast income gains. No longer can my sims write a book in one day, and a masterpiece takes them almost the whole day to complete. This way it takes more time to make money, slowing down income and having it feel more authentic.