Space2001,
1. I don't really think HD-DVD is going to be out that soon...
2. Depending on quality, you might want to consider it (it'll probably be backward compatible, so you might want to consider replacing just the top of the line movies).
3. Up until now HD scalers were unaffordable for the mass public.
4. In CES, we're supposed to get a glimpse of two (or three) new HD scalers - aSimilator and HD LEEZA (I'm not sure if Rock Pro scales HD or not).
5. Prices should be around $4000, so they're definitely getting affordable.
No one I know has seen either of these units, so we don't know what they're capable of, nor have reviews of them. These products were hashed many many times, so you can do a search.
6. No matter how hard you'll look, DVDs can never be made to look like their equivalent HD transfers. It's just the facts of life. HD has more information, therefor - it will look more lifelike, have more detail and be more 3D.
I dare say that even Hd doesn't scratch the surface and that within the next 20 years, we're bound to get a few more format shifts. This is a starteling contrast to the last 50 years which had one significant format shift in video brodacasting (the addition color), a few in sound (stereo, then prologic, then 5.1 and more recently 7.1) and a few in storage (video tape recording, optical-digital and recently DVHS).