I was hoping someone could take a critical eye to an idea i've had.

Traditionally it's said that one should diversify across various asset classes and ultimately types to spread the risk out based on their preferred asset allocation.  In theory, one should then periodically rebalance their portfolio and potentially scalp the gains from winners and feed into the losers.

Today I was thinking... What if instead of diversifying across a basket of assets you just invested in two ETFs:

 1. TNA - Goes 3x long
 2. TZA - Goes 3x short

For shorter term periods could you simply hold these two, and rebalance them on say a weekly time frame? 

Another idea I had was that since traditionally the market goes up you could over weight the long position.  

Thoughts?

thanks!