I managed to pick up a Sony Wega CRT that's 100% SD. It was made in 2004, but it can't even do 480p. Two observations:
1. The dumb thing has an RGB input, but it forces certain video settings while in RGB that prevent me from turning up the color, and the picture looks extremely washed out and dim, by anyone's standards. It doesn't do that with its component input, which is why RGB converted to YUV actually looks much better. It really goes to show you how for all the fuss about one signal type versus another, the TV itself is the most important factor.
2. True SD TVs definitely look different. It had been a long time since the last time I had seen real scanlines. Which is better for 240p games? Well, it's a toss up.
On one hand, the true SD set offers a kind of softness in places where an HD CRT looks rather harsh. I was using the Kordamp's 240p test suite for a side by side comparison, and Sonic 1's clouds definitely look better on the SD set. Using component or RGB still allows for a very nice picture on the SD set, yet the pixels aren't as jagged and the color gradients look more smooth.
On the other hand, the HD CRT passed all the tough tests much better. The color bleed check, the checkerboard pattern...even when flipping through full screen red/green/blue/white/black, the HD set made the transitions instantly, while the SD set always needed a split-second to adjust.
And frankly, I think a preference for scanlines must be purely a nostalgia thing. And I can feel some of that nostalgia, believe me. But at the end of the day, I'd usually rather not have them.
I do have to admit one more thing, though: 480i looks slightly better on the SD set. It's not quite as shaky, and the interlacing is harder to spot in horizontal scrolling.
Does this imply that I should get an SD widescreen CRT instead of an HD one? Maybe so. I better chose, though, because I'm about out of space in my gaming room, and my girlfriend is going to wring my neck if I keep bring home giant CRTs.