My thought is, "WHY?!?!?!"
Gadgets do not make a better gun necessarily. I do not recomment laser sights, compensated barrels, etc.
THE FIRST THING YOU SHOULD DO is spend $20 and 2 hours to purchase and read Dave Lauck's book "The Tactical 1911." This will give you the best base to understand what you should do and why because it all depends on what this gun is to be used for.
$400 will go quick. For any type of defensive pistol need, I would recommend a Commander hammer and beavertail safety, an extended hammer safety, and low profile sites like a Novak or similar. Buy new sets of Wolff springs (18.5 lb. variable recoil spring is recommended). MOST IMPORTANT though would be a $100 trigger/action job from a reputable 1911 gunsmith...preferably a member of the American Pistolsmiths Guild (not many are). Teddy Jacobsen in the Houston area is highly recommended.
To be honest, you can buy a good used Springfield with most of this on it for $500 at a gun show. Then you only need to spend an extra $100 on a nice action job.