Never commute to reserve when you have an opportunity to not commute. The pay rate is higher on the 320, but I'll bet you'd come out about the same after adding in expenses for commuting. Save yourself the hassle and sit short call at home!

Edit: Whoops! Misread your post and missed the part about holding a line in DTW. I'd still be inclined to not commute. Out of 22 years flying for the airlines, I've commuted for about half of it. It's certainly a personal choice, but based on my experience I think not commuting is BY FAR the better choice. Sitting reserve at home is not that bad.