My on-the-record answer is that first aid is almost always worth it. It's fast, easy, and cheap to max out, and you never know when it'll come in handy. Paired with any kind of stun, root, etc. that will take the mob out of commission for a couple of seconds, a bandage can be a lifesaver. I gouge + bandage all the time to save my rogue's butt - it's almost like playing a druid and being able to pop out and heal, except not as good, cause a rogue, really, is a gimped druid, but I digress.
Always unable to take my own best advice, I never leveled it up on my druid. I've never missed it (druids have plenty of panic buttons) and I'm greedy when it comes to selling cloth.