The possibilities of modifying a 1911 are literally endless. I have been seriously looking at picking up a RIA GI just as a project to build a race gun. From everything I've read on various forums, they are a great buy out of the box, but again, every 1911 can be improved ou of the box.
Some ideas I have in addition to sights and a beavertail are fitting the slide, replacing the barrel with a Nowlin or Barstow gunsmith fit barrel, trigger, fitting your sear/ hammer to have a perfect neutral fit, lots of polishing in critical areas, extended slide release, extended mag release. That's enough to get you started in about a grand worth of needed tools alone not counting parts. The real answer is shoot a few hundred rounds through it, then start making changes so you can see what you like and what you don't. Unless you are building a race gun, you should start small.