I think the difference between LCD's boils down to what math they use to convert the image. Better math requires better hardware to run it and therefore costs more and may require liscence for the code. It's kind of like how you get HQx4 or other up-scale effects in an emulator. At the moment some manufactures see the up-scaling as an important feature and invest in it, some don't so much. As time goes on the hardware will become cheaper, but the interest in non HD will decrease. So stockpiling CRTs, if you've got the space, would be a good idea. Otherwise get a good stand alone up-scaler.
I've seen videos on YouTube where they use a scan-line generator in conjunction with the up-scaler, which goes a long way to re-creating the look of a CRT. But ultimately the best picture you get on an LCD is the best re-construction of a crt any way.