As a former E92 335i owner, I think there are a couple of reasons to go for 320i:
1. In Europe the price difference is €8k between the 320i and 328i. If you go from a 2006 car to a 2012 car and you have a €10k budget, it's quite a step to raise that budget to €18k. Just became a daddy, so I can use the €8k for other (more important) things
2. Because there are less 328i's sold in Holland, the price difference for 2nd hand model is even bigger.
You can buy a full-option 2nd hand (1 year old) 328i for about €45k. A full-option 320i (same options) can be bought for about €36k.
3. 320i has an A label (less taxes and monthly costs when leasing the car)
4. 184hp is plenty for the Dutch roads. You don't only buy a BMW to go fast. You buy one for the great handling, sporty feeling and luxurious feel. Our speed limit is 120-130 km/ph. I rather put my money in a wide screen navigation, sport seats and leather than in more hp. Also because of the strict speed limitations and high fines.
5. And if you really want to go faster, for about €1k you can tune your 320i close to the output of the 328i engine.