
Each investor has a different level of return they will be targeting. The level of return that you will target will primarily depend on the level of risk you are comfortable taking on. Generally, with investing, the higher the risk, the higher the potential return. This maxim can be true for all manner of equities and assets, including art collecting.
One way of determining the level of risk and return you are comfortable with is to understand the returns you might expect to gain from other assets, like stocks, bonds, property, and precious metals.