The cacti generally bloom in May, so I don't think you'll see that. We have had some abnormally warm weather the past couple weeks (mid 80s), so you might see other plants blooming.

If you're coming from the east coast who knows if you'll get another chance to visit Organ Pipe. I say do it. It's just a couple hours from me so I can always put it off (and then I never get around to it ).

As far as the border patrol, there are a lot down there (like every other car). I've never had a problem at the checkpoints; it's usually one or two random questions that give the nearby drug dog enough time to take a quick sniff. The longest I've spent stopped in one was maybe 10 seconds. I've never once had to show ID, reg, etc...