I have a khaki trench, although it's a bit more dressy than a usual trench as it lacks a belt. It's from the old Marshall Field's line. I don't wear it a lot. It's a miracle if I wear it twice a year. My wedding and funeral coat. I'm sure I would wear it more if it was more casual looking like a normal trench. But I think it's one of those classics that you just gotta have in your closet. Another consideration for me in buying it is that I'm short and it's darn hard to find coats, especially trenches, tailored for short ladies. I had never before found a trench that didn't look just plain stupid on me. This one required only a small bit of hemming and tailoring, so I had to buy it.
If you're considering a trench and you found one that looks good on you, I say buy it. Everyone needs one in their closet.
I have a friend who wears trenches regularly for work and nights out. But she's more fashionable than I am.