It's a gamble either way, Alvarez... If I were in your position, I'd go ahead and jump on the HD tivo. That way you can use it while you are waiting on the dust to settle on the new sats and new HMC boxes, etc, etc.
Eventhough no one can guarantee what the upgrade offers will be, and eventhough D* is getting crazy with their increased rates for ST you have to expect that they will make it enticing to stick with them. They are getting too much competition from cable and E* now.
Enjoy the HD tivo, and just watch for the upgrade offers to mpg4 equipment to arrive.
/cr0mag