I suggest that you try turning you dynamic iris ON and spend some time with the calibration disc to see if you are maybe happy with what you have. The only reason to turn off the dynamic iris is if it is not designed that well and you are annoyed by the pumping from light to dark scenes. Turning the dynamic iris on should certainly help with both black levels and shadow detail (the two most important aspects of the picture). Since you have a plasma you are probably a little bit spoiled with good black levels and shadow detail (especially if you have a Panasonic or Poineer), so you may not be happy with your current projector. If that is the case you will probably need to look into a Sony or JVC projector. They seem to be running neck and neck in terms or price and performance and most other projectors can't get near them in terms of black levels and shadow detail in their price range. The Sony's have a very well designed dynamic iris that helps get the blacks, while the JVC does so without one.
My vote if for you to hopefully get a projector that you are happy with. Unless you can afford a 100" plasma, you just will not have that impact factor of a huge screen that you can get from a projector. But, like I said before, see if you can be happy with what you have. Epson makes some good projectors. They are supposed to be pretty good in terms of black levels and shadow detail, but only if you have it set up right (though Sony and JVC are probably going to be a bit better).