If the lenses you have work well enough, and photography is just a casual hobby, why spend more?
First, you'll get 3 primes everyone recommends = $1500. Then, you'll start talking about bokeh and rendering. You will compare the image quality to the Tamron and decide you need something a bit sharper at the long end = $750 and/or $1300. Then you will want go a bit wider, so might as well go for it with the 10-17 fisheye, or the 14 or 15, or Sigma 10-20 = $500+. Or the 12-24 which is an excellent focal length range = $700. And if one of the limiteds is not a macro, you will probably decide you want a macro = $419 (Tamron 90 with rebate).
You sir, have opened a can of worms :-)
Oh, yeah, forgot about that faster 50.
Last edited by SpecialK; 05-18-2010 at 10:13 PM.