Other non-writer friends will soon lose interest in the story of your umpteenth fight with your parents, but start talking to your writing friend, and watch his/her face light up. This is because while you're unburdening your soul and engaging in free therapy, your writer friend is already mining your life for the his/her next story. Win-win!
A committed writer is a voracious reader, and one side-effect of reading extensively is that you end up learning and knowing a lot. If you need a source of random trivia, in a pinch, you can ask your writer friend, and chances are, you'll find what you're looking for. They're also the ones most likely to be able to answer those questions that start with “why?”
Just got dumped? Didn't get that job you had your heart set on? Your internship supervisor trashed your thesis proposal? Your other friends don't “get” you? Never fear, talk to a writer. Anyone who has had to face criticism for a piece s/he has laboured over, had to endure multiple re-writes, and still got no love from publishers knows what rejection feels like, and will definitely be a lot more tolerant with you.
Whether it's that birthday note you want to save in case they make a movie about you, or the perfectly penned excuse note so that your teacher doesn't punish you for missing homework yet again, having a talented wordsmith amongst your friends is a gift that just keeps on giving.
You don't need to fête your writer friend for him/her to have a good time. Nor would you have to deal with scheduling gymnastics in order to spend some quality time. They're low-maintenance, and usually have a flexible schedule, so even a low-key hangout is just fine by them.