I fully agree with the importance of a quality gun belt (unless you pocket-carry). I've never invested in a $100+ gun belt, but VersaCarry offers several high-quality options for little more than the cost of a department store leather belt (usually $30-$40 depending on what's on sale).
I prefer tritium night sights on all of my carry guns, but I'm also fine with a good set of fiber-optic sights or high-visibility paint/nail polish for revolvers. My extra-mag holders are my pockets, and they work equally well with magazines and speed-loaders.
As far as grips, I have never upgraded or modified the grips on a polymer-framed gun. I wouldn't buy a gun to use as a carry gun if the grips did not provide adequate traction. For metal-framed semi-autos, all of my grip changes have been for aesthetic purposes or to make the grip slimmer to aid in concealment. The grip changes I've made to revolvers have usually been to make the grips shorter/slimmer/longer to improve concealment or handling. I don't believe that I've ever changed grips strictly for the purpose of adding traction/texture.