the change in wheel diameter can cause changes in your alignment readings, for the cost of the alignment compared to the cost of replacing your new 16" tires if they show bad wear quickly, I would get it done.
it will not affect your alignment. The suspension is still in the same point of its travel so nothing has changed. Frequent checking for missalignment and correcting the alignment on time is very important though!Hope this helps.
I beg to differ with you b18bad, the change to 16" rims will change the alignment angles. The new wheels will have a different offset and the footprint of the tires will be different, this causes the suspension angles to change - giving premature tire wearout.