There is a lot of talk about diversification these days; especially when the market gets very competitive or the profits start to drop.
If you have six areas that you understand well then your are doing a great job, if not slowly increase you expertise to six areas and become expert in them.
You will find this is enough to keep you busy. If you still have time at you hands and want to diversify more then go ahead why not. However be careful and do not over diversify otherwise you will not specialise in any of the area and may miss out on golden opportunities that lie with in them.
As the old saying goes: Jack of all trades and master of none!
Here’s what Warren Buffet has to say about it. Although he talks about the stock market this could apply to Affiliate marketing (Skip to: 1:13 to go straight to it)