I think buying retail lots or restaurants is the best option. First, because they cost a lot up front. Second, it feels more like your sims are expanding instead of just finding a way to start over. We really need more ways for our sims to spend money in an expansive way (vacation homes, boats, cars, etc.) as well as a contracting way (lose money in an investment, etc). Something that provides more gameplay that is a motivation to earn the money, not just starting all over again from the beginning.