What temperature range is suitable for grill smoking?
Don't let the tail wag the dog. When smoking, you want to figure out time and temperature first and worry about smoke second. This can obviously vary widely. That said, there are things you can do to get more smoke going:

If you can smell it, you'll get some smoke flavor. If you can see it, you'll get more. If you're not getting (much) visible smoke then you need some combination of 1) wetter wood 2) lower temperature 3) larger wood. You get less smoke when the wood just goes up in flames. Chips are particularly prone to do this. Larger chunks smolder better. Things also smolder better when they're very wet or the fire isn't so hot. But again, you want to figure out your temperature and then get smoke, not make large temp changes just to get smoke. 

If you're doing very low and slow (225F), sometimes that's not enough heat to get your wood smoking well. Smaller chips or higher temperature are the only things I've found that really solve this problem.