Replacing CRT RPTV with Flat Panel
You are absolutely correct that CRT-based displays have much deeper blacks than virtually all plasmas, except the late, lamented Pioneer Kuro. If black level is very important to you, you won't be happy with the Panasonic S30. Your best bet is an LED-illuminated LCD TV, which can achieve far better blacks because the LEDs can be dimmed.
Such TVs come in two varietiesbacklit and edgelit. As these names imply, backlit sets have LEDs in an array behind the LCD panel, while edgelit sets have LEDs positioned along the edges of the screen. LED-edgelit sets are much more common because they are generally less expensive and can be made extremely thin, which is very popular with consumers. However, most suffer from uneven illumination in dark scenes, which I find very distracting.
LED-backlit sets are more expensive and not as thin, but they can offer a feature called local dimming, in which the LEDs behind dark portions of the image are dimmed while the LEDs behind bright portions are brightened. This greatly increases perceived contrast and lowers apparent black level, though it often causes halos to appear around very small bright objects on a dark background because the dimmable zones of LEDs are much larger than pixels.
The only LED-backlit LCD I know of that does not exhibit haloing is the Sharp Elite X5FD, but the 60-inch version lists for $6000, which is way more than the Panasonic TC-P60S30. (See our review of the PRO-60X5FD here.) Sharp also makes other, less-expensive LED-backlit LCDs, but they do not offer local dimming.
The best choice that comes closest to your price rangethe TC-P60S30 lists for $1600is the Vizio XVT553SV (shown above with your Sony RPTV), which lists for $2200. This set uses LED backlighting with local dimming, and it garnered Top Picks status in our review here. Vizio makes several other, less-expensive 55-inchers with local dimming, but we haven't reviewed them. Even with LED backlighting and local dimming, the XVT553SV probably won't achieve quite the black level of your Sony CRT-based RPTV on real-world material, but it will get much closer than the Panasonic S30.
As for picture quality, as long as the Sony RPTV is properly converged and calibrated, the picture quality is probably great, though it might exhibit some hot-spotting and not look as good off-axis. The picture quality of all LCDs suffers as you move farther off-axis, a problem that plasmas do not share. (The Vizio XVT553SV is better at this than most LCDs we've reviewed.) Finally, your Sony has no HDMI inputs, and high-def component outputs are disappearing from Blu-ray players, so that will be more of a problem as time goes on.
If you have an A/V question, please send it to firstname.lastname@example.org.