Does the breath weapon give a 24h-immunity? If not, it's even better, and if yes, you can breath on the party early in the morning till they all make their save, so that later on you can include them in the area of effect with little care.

I like it when Undead actually have meaningful things to do at more than low levels. You could also gain infinite electricity damage with Undead Meldshaping and a soulmeld somewhere, couldnt' you? This would free up some class levels to go into something more interesting than Sorcerer.

No idea on whether the proposed negative LA/reduced HDs are accurate, but it's at least tempting to try one at 13 RHD.