cguzik

In addition to the points that have already been noted (wait until you have a solid foundation in one art, choose complimentary arts), it is important to consider the teaching methods in your prospective new art in the context of the goals of your practice.

Consider the art, and what you hope to gain from its practice. By picking it up, as suggested in the thread title, you could be making a lifetime commitment. You have to ask yourself if you can make the commitment required in order to gain the results you seek.

It is a worthy goal to seek to improve particular skills such as punching better, cutting better, breathing better. However, to find these things within certain arts will take a lot of study. In fact, you can pick any of these skills and find arts which to a large extent focus on perpetual improvement of that particular skill. However, the path of study may require substantial mat time to get particular subtleties that make all the difference.

You should also consider whether those same things you seek can be found within aikido.

I had been practicing aikido for about seven years when I started practicing iaido