Nate,
Your logic is good.
I just got an HD-DVD player and now have seen the holy grail....
By the way HD-DVD does 1080p also, if you get the new higher-end Toshiba unit HD-XA2. But all source material on HD or Blu-ray is 1080/24 or 1080/30 anyway,
so it doesn't matter if you have 1080/i or p, as long as your set properly deinterlaces.
Even my 720p set looks noticably better with hi-def, so I imagine a 1080 set really shines.
I hear the SXRDs are not optimal with SD sources, so that is another consideration.
Pete