Don't have a lot of time here, but here is a quick response:
You make a good point in some ways. Perhaps the SR against the curative stuff should be rolled openly, but maybe not. Failing an SR roll on a detection spell is no different, to my mind, than the rogue failing a search check for a trap. Also note that the PCs should definitely be aware if this spell exists in a given campaign setting, unless having invented this spell is going to be a MAJOR shtick of a MAJOR villain in the setting.
As for curing ability score damage or returning someone to life, the additional restrictions (a minimum caster level) only kick in if an ability score is reduced to zero or the character dies of a poison (some poisons might still exist somewhere that deal hit-point damage or literally list "death" as their effect). I suppose I could specifically say that "This has no effect on the effects of Restoration, Restoration, Lesser , or Restoration, Greater or similar spells, to the extent that they restore damaged or drained ability score points. If a spell (such as Heal) both restores ability score points and removes poison, then the restoration effect happens as usual, but the poison removal effect happens only if the poison's/ravage's SR is beaten."
P.S. What is so horrible about the rules for detecting poisons? If you mean by MUNDANE means, this actually isn't supposed to do ANYTHING to counter that except sometimes fooling you into thinking that the person passed the initial or both fortitude saves. If you mean by magical means, yes, this is a 5th level spell that provides some protection against some 1st level spells... I see nothing wrong with that.