Attracting Wealthy Sims to your town is the easy part; however, keeping them around is tough because Wealthy Sims are more sensitive to their needs and vocal when ignored. "Education, pollution reduction, better crime suppression, and consistency in all your services will become a priority as your Sims go up in wealth," EA says. A dearth of disasters probably helps, too.
Another crucial aspect is increasing land value, a byproduct of putting services and public transportation systems in place. As you build infrastructures, you'll start to shape your city and attract the corresponding kind of Wealthy Sim. It's key to build parks around your residential areas, giving the Wealthy Sims a much-needed place to go and offer condescending looks at the other, poorer Sims.