Of course the Hamdi case is important…but not as important as the Padilla case. Although I think the government's position in Hamdi is wrong, the threat posed by the possibility that the government might grab people abroad and falsely claim they were in the field of battle, or even hold those truly in the field of battle for a long time are problems that are survivable. Letting the government disappear citizens domestically (Padilla) is not.
Update: I should explain that I don't mean by the above to suggest anything about the facts of the Hamdi case. Rather, I mean that if one were to accept the government's contentions in the Hamdi case, then cases where the person detained was abroad, but not on the field of battle, would be unreviewable in the future, which strikes me as pretty darn bad — but not as bad as making the whole US a zone where any citizen can be picked up and locked away for ever by the (un)secret police.