First off, additional lenses won't improve your pictures. They may give you different perspectives, but not necessarily "better" images.

I aay this over and over. It's good photographic techniques and a vision that will help you create a well recieved unified body of work. Good composition, proper exposure and using a tripod will give you the best images.

As for purchasing additional lenses, If it were me, I'd not go with that wide a range because the image quality probably wouldn't be as good as with a more limited range zoom. But if you're looking for a one lens to do it all, that may be the way to go.

I'll leave you with this thought. I once owned the Nikon 35mm - 200mm zoom lens and traveled to Austria with a two lens kit. The 35 - 200 and a 20 because they gave me a wide range with a common filter size. I came back with images that sold for years, but I used a tripod for every photo and lost whatever spontaneity I might have had with small faster single focal length lenses.