A helmet is a good thing to wear if you want to survive an accident. It amazes me that "nobody" wears them in Europe outside of Germans. I will sometimes ride around town or a bike path without a helmet, but only on quiet roads and bike paths. I always wear my helmet on my commute.

Helmet lights are good for three things -
1. To light in a direction other then where my bike is pointed. I have used this to see arund a turn, to see a person/animal that might step into my path, etc. Granted this is really only useful in dark areas. In a city I don't really need a light for this (or any light to see...lights are to be seen in a well light city)
2. To be seen - a helmet light is higher up and can be seen by the bit tall SUV that pulls up next to me - they can't see the bar mounted light as it is bellow thier window. Maybe this is mostly a problem in the US were big trucks and SUVs are more common.
3. To get a drivers attention - shinning my helmet light at a driver or their mirror is a good way to get their attention (I try to avoid in the eyes but sometimes they are looking the other direction). This is useful in an urban environment, when going through an all way stop, etc.

Just because you think a helmet light is not needed in your situation doesn't mean its ridiculous.