You forgot to preface that with "In my opinion". It's pretty clear that it's still good law.
"Every President since it was passed has treated it as such. "
Yes, that's the problem and that's how we end up entangling ourselves in places we have absolutely no business being - Kosovo, Somalia, LIBYA etc, etc.
Clinton has made it pretty clear that if wasn't for the abortion that was Operation Gothic Serpant, he would have unilaterally intervened in Rawanda. Wouldn't that have been swell?
So, if we have presidents that ignore US law for long enough, those laws become dead letters, or something?
Maybe Posse Comitatus is unconstitutional too? Should presidents just ignore that as well?
We need to get back to some basics. If there's not enough popular support to get a congressional authorization to involve ourselves in some military engagement in a faraway land, then we shouldn't do it. We have got to STOP indulging a President's personal whim to play world police.