When I had the 2-1 hard downshift I always switched to N and still do it sometimes due to the habit I got. If you do it everyday it becomes a habit and you don't forget to put it in D when the lights turn green (similar for manual drivers).
Now, going to 2nd from the start to avoid switching to 1st might be an option although the adaptation feature should do that for you. The driving adaptation values are changed based on the driving style, so the car shouldn't switch back and forth gears if for the last few little while it was doing that. It should keep it in one gear.

Do you save on gas going to Neutral? it sure it does but probably not a lot. Somebody mentioned earlier that the rpms go higher if you go to N. There is a setting for that. You have about 4-5 rpms settings if I remember right: idle, idle with AC on, idle in D, idle in D with AC off, idle in D with AC on... If your car goes to higher RPMS when in idle then it is set that way.
I used INPA to monitor a few values in my tranny while driving and one of the parameters was 'load'. When I had the car in N that value was low or zero. When I put it in drive with zero increazed rpms I had a load value and when I had the idle rpms set to +50 or 100 it was even a higher load which you would translate to more gas overall.

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4.8is 2004 imola red
4.8is 2005 Black on Black - DINAN/2 sold
4.4 2004 X5
2003 330xi
2008 328xi - sold
4.4 2000 X5 - sold