Probably the highest quality solution to your problem is to buy a second DirecTiVo for the bedroom and run extra cabling from the sat dish to the second DirecTiVo (although this may require one of those multiswitch things). This also lets you record that many more simultaneous shows, plus you've got another digital audio out, which would let you do 5.1 Dolby Digital from the DirecTiVo in your bedroom (assuming you want Surround Sound while in bed and you don't mind adding the amp and speakers).

Then, the only question is whether you'll be happy with a non-HD plasma. As you point out, though, it will be fantastic for DVD watching. You may well be quite happy with SD in the bedroom and HD in the living room.

(edit: changed "HD in the bedroom" to "SD in the bedroom")