The way I see it, one of the best ways for a person to grow as a person is to experience and learn new things.
In the martial arts, it's not good to just stick with one martial art and never try any other for the rest of your life. It's usually recommended that by brown belt or ten years training to try a different martial art or school. For instance, if you take karate and from a good school, you are now strong with basic punches, kicks, and blocks. You are good at moving from your center and keeping your balance. But you haven't learned how to lose your balance, and how to use that to your advantage. You haven't learned [many, or any] throws or grappling. So as you become proficient in karate's basics, you start over from the beginning and learn something new. Then, when you go back to karate solely, you have a much deeper understanding of how the body works, a new mindset from a different style entirely (you'll wonder why aikido throws work the way they do, even though it seems so illogical, for instance, which only comes with training it). You can approach the techniques in a different way, see it from a different perspective, and have so much more to add to your training.
Not only that, but there are drastically different cultures involved in various martial arts, which cultivate the mind. Maturing your mind is the best way to advance in the martial arts, as it leads to a calmer, thoughtless reaction in a fight. I get a little disappointed when I hear people say they're fine with who they are and see no reason to change themselves. It's okay to like who you are, but is that a reason not to make yourself a better person? Oh well... ramblings, ramblings.
This applies to writing, as it does to nearly everything. There are some genres of writing that are very hard for certain writers to write. It's great to be strong at fantasy and have no ability for romance. But as I see it, trying your hand at romance can enhance your fantasy. It can take a long time to get proficient at romance, where as fantasy may have been easier, but the I personally see long-term potential in honestly trying your hand at everything.
It can take 10-15 years to become proficient at one martial art and it's always a hard journey. It will take a lifetime to polish the diamond and longer if you can only see one part of the diamond, or have only one tool. Get more tools and a wider view, and making the diamond shine becomes much easier.
So, long story short: I recommend writers try their hand at other genres, but only after they know they're good at their current genre. It gets rid of your ego-- you're good at one thing for so long, it often breeds it-- and shows you that you're still a n00b at writing in some way or form.