Let's examine what the postdoc is and the need for multiple postdoc positions. A postdoc is traditionally a "training phase" of a scientist's career, typically performed immediately after graduate school. But since there are so few professorships currently available, a career inside the ivory tower may not be a realistic option for many, so it is important to ask yourself: Does one postdoc make sense, let alone two? 

There are a few reasons to do a postdoc:

1. Because this is the right next step for you, that is, you want to. 

2. To prepare yourself to become a professor or, in general, for the next step in your career. 

3. To get additional training, either in your field or another.

Now, let's discuss why you want to do another postdoc. Is your lab running out of funding? Is your project not moving? What is the end goal? If you answered that you want to be a professor and no other job appeals to you (and you think this goal is reachable), then yes, you should probably consider another postdoc. If you want to become a professor, a successful postdoc period is the backbone for your career. If you feel your first postdoc isn't enough for some reason, and the professoriate is your end goal, then consider a second postdoc. 

Consider carefully how you would like to spend the next few years of your life. Are you willing to live on postdoc wages for a few more years? Consider both the financial and career implications of doing a second postdoc and don't forget to consider all available options such as teaching or industry postdocs. 

Don't forget to keep in mind, if your end goal is not to become a professor, then a postdoc, let alone two, is probably unnecessary.