'It's a nudge in the wrong direction. Not a leap, but definitely a nudge.'
I'm open to that argument, but for my own part I can only say that my objection to the ruling is really an objection to the drug laws themselves. I have a residual sense that even though marijuana is technically 'contraband', there's still something illicit about sniffing for it because I don't think it really _should_ be 'contraband'.
If the contents of the trunk had been a pony nuke, I think we'd all have a different opinion.
This is a separate problem with the legal system -- it fails to properly calibrate the definition of "reasonable search" to the case at hand.
I'd have no problem with a legal doctrine that says that the cops need less evidence to search for (e.g.) terrorist preparations than to search for (e.g.) somebody's pot stash. Of course, the doctrine would need to be backed up with corresponding exclusions (e.g. if the cops went in looking for a pony nuke based on minimal evidentiary support accepted in such cases because of the public safety issue, didn't find a pony nuke, but did find pot, they can't use it even if it was in "plain sight" once they got into the house).