As stated the noise figure of the amplifier used will change the signal amount. The problem with this is unless you have a way of measuring the signal to noise level at the antenna location there is no way to calculate the signal to noise ratio of you signal at that point even if you know the amplifiers noise figure. The RV-3090’s noise figure is about 4.0dB average across the amplifiers range of 54-806MHz (channels2-69). What we're saying is that in order to have a good signal to noise ratio you need to use amplifiers with a low noise figure. The noise figure of the newer antennas may be about .2 to .3dB less which will not make that much difference in you signal to noise ratio.
As to why your picture is different with the new TV set verses the older one is it could be the sensitivity of the newer TV may not be as sensitive as your older set was.
It is further confusing to the consumer because recently the FCC chairman commented on the smaller DTV coverage area may require that some viewers will need a preamplifier to "boost" the DTV signal. Since the DTV signal is lower in transmitted power as compared to the analog signal, station engineers have noted how sensitive these lower signals are to amplification so they avoid the complication of the signal amplifier.