Not a replacement, more a complement.
The 50mm is a useful lens, but its not very wide. Having a prime lens can be good for your photography as it makes you move around a bit more instead of just zooming.
50mm on a film SLR is known as a standard lens, as it has a similar field of view to the human eye. However, with the DSLR crop factor, this becomes 75mm or thereabouts, which is significantly longer. If you wanted a prime lens to rpelace the kit lens as a all-round lens then I would suggest something like a 28mm or 35mm lens.
HTH.