What I've resorted to doing to...
Download Nvidia Inspector. This is a great tool that allows you to actually turn on graphical features not found in games. Not going so far as HDR, or Bloom perhaps, but things like ambient occlusion, extreme levels of AA, and AS. I've tried many of the ENB series addons got one to work for GTA, but it just came out extreme for me, over saturation of light sources, turning off HDR helped, but was a tad to dark. I'm pretty happy using this inspector tool, while it's not good HDR, or Bloom, the ambient occlusion seems to mimic it well enough. There is a little tool icon at the end of driver version, that opens up a bunch of goodies you can turn on in your games.
http://downloads.guru3d.com/NVIDIA-I...load-2612.html