I'm gonna go along with the "if it ain't broke, don't fix it" approach.
Do you plan to shoot a lot of different loads? Then you don't need adjustable sight -- get it shooting where you aim, and stick with one load and fixed sights will do just fine.
New springs -- basically just the recoil spring -- ever 5,000 or so rounds is a good idea. The standard spring is 16 lbs, some people like to go to an 18 lb spring.
Recoil buffers are iffy -- some guns won't function reliably with them. My carry gun is a Kimber, and Kimber advises against recoil buffers in their pistols. My old carry gun was an Argentine M1927 (a M1911A1 made in Argentina, on Colt machinery under Colt supervision.) It would not function reliably with a buffer installed.
Extended safties, slide lock and magazine releases are popular, but I never found them worth while in a carry pistol. The downside is, extended controls can be activated accidentally -- for example, you can drop a magazine or activate the slide lock accidentally.
Extra magazines are a good idea -- I always carry at least one loaded spare, and preferrably two. I like Chip McCormic "Shooting Star" magazines, and find the 8-round versions function perfectly in all my M1911s.