Do it For Your Soul - Collect the art that impacts your soul language and trade your money for it so that you can enjoy the visual poetry over a lifetime.
Do it For Your Bank Account - Ignore the art and pay attention to the rise and fall of an artists prices. I'm sure that, as in stock investing, there is a good amount of due diligence involved here.
Do it For Your Ego - Listen to what the important art people are saying and do what they tell you to do.
Do it For Your Decor - I'm not even going to go here, but I understand... I understand.