Component always gives the best picture (unless you have DVI or HDMI), but if your monitor doesn't support it, I wouldn't bother upgrading to it. I don't think you will see any benefit by having the AVR convert the signal from component to s-video.
When you get your new plasma definitely hook up the component from the DVD player to the monitor. If you only have one device that outputs component video, there is no need to go through the AVR if you don't need to use it for video switching. You'd be (a) buying an extra cable and (b) risking a signal downgrade.
But it seems that the cable box is the weak link in your set-up. The video quality while you are watching cable will never be better than the composite signal coming out of the box. The Replay doesn't up-convert/up-sample the signal, it trans-converts it.
I'd call the cable company and see if you couldn't get a newer box with an S-video out, unless you will be going the high-def route when you get your plasma.
Then you could use the AVR for component switching, just make sure your AVR model supports the high bandwidth required for high-def.
When you get your new plasma definitely hook up the component from the DVD player to the monitor. If you only have one device that outputs component video, there is no need to go through the AVR if you don't need to use it for video switching. You'd be (a) buying an extra cable and (b) risking a signal downgrade.
But it seems that the cable box is the weak link in your set-up. The video quality while you are watching cable will never be better than the composite signal coming out of the box. The Replay doesn't up-convert/up-sample the signal, it trans-converts it.
I'd call the cable company and see if you couldn't get a newer box with an S-video out, unless you will be going the high-def route when you get your plasma.
Then you could use the AVR for component switching, just make sure your AVR model supports the high bandwidth required for high-def.