Agree with all here, FI is probably the most rewarding rating I have to date. You get to meet all sorts of people, it'll test your patience (oh my goodness will it test you!), and you fly for free, or better yet, get paid.
I've also realized how much I've learnt myself over the years, which is good for the ego department. It may help you forward to the elusive job.
And, as someone mentioned, FIs have been regarded rather highly by airlines.