The Sporelings like shrubberies a lot; bring them enough of them, and you'll be exalted.

This is where being able to stealth-farm helps. Sanguine Hibiscus is a ground spawn in Underbog (as well as occasionally dropping off any mob there); normal Underbog is low-level enough that a level 70 can pick most Sanguine Hibiscus nodes available in the first half of the instance (before the Naga packs start), using stealth judiciously to avoid having to get in combat with mobs.

There are 13 nodes in the accessible half of the instance, 12 of which can be picked without much trouble; once you have picked the lot, you stealth back out, reset instance, rinse and repeat. (The numbers come from the nice guide found in the comments for Sanguine Hibiscus on Wowhead; they do match my observations in that I average 11-12 per run if I just pick ground spawns and then reset, but I hadn't bothered counting or mapping spawn points.)

So I started picking Sanguine Hibiscus. Pick, reset, pick, reset, pick, reset... this is boring. I wonder if I can kill some mobs for a chance at extras, plus greys, the occasional green, and ability to open the chest in the corner near the start?

Turns out I can. :D

I would imagine this would be impossible to do as a rogue, or even as a non-feral druid; I still die sometimes when things go wrong (I don't dodge enough, I don't crit enough, I don't Bash in time, etc). It does, though, pay for itself - 5g+ from the chest in the corner when it's unlocked and the mob pack isn't in a configuration that's impossible to clear (more on this later), plus whatever greens / blues might be in the chest (I got a blue from it one reset; it remains to see if it will sell on the AH), plus greys / greens dropped by the mobs you kill.

I do this in DPS gear, but in bear form. My gear is... amusing... right now, given that it's part blues, part Hyjal drops - and it's sub-optimal for this kind of thing, as it's raiding-oriented (so aimed towards being at the hit cap first, as opposed to wringing slightly more attack power out of it); I would imagine anybody in decent blues can do something similar.

I would also imagine this would be far, far more profitable if Herbalism was one of my professions - the amount of Ancient Lichen nodes is pretty high (and most of them are near the Sanguine Hibiscus spawn points, so they could be picked without touching a single mob), plus almost every mob killed can be herbed.

Either way, here's a quick summary of the mobs you will face.

Bog Giant
Hits hard, can put (if I remember correctly; it almost never happens at 70, you'll resist most of them) a Nature-based DoT on you, enrages at 25%. You'll want to fight these alone (no, the two-pull before Hungarfen is impossible), with Frenzied Regeneration off cooldown in case you dodge too little and your health goes down faster than that of the mob. Having a near-full rage bar when it enrages helps.

Underbat
Easy. Squishy as hell, can be Hibernated, no special abilities that I can recall. In multi-mob pulls, you should always Hibernate one. There are two right at the entrance that can be pulled alone, but after that, they're almost always part of a mixed pack of three mobs (there's a four-mob pack of only Underbats just past Hungarfen).

Underbog Lurker
Enrages upon entering combat, goes back to normal at 75% health. First priority when these are in a mob group should always be to get them to un-enrage (with one exception, detailed below). Always part of a mixed pack of three mobs.

Underbog Shambler
Also known as "oh, no, not that little bastard again". It heals. Often. (Far more often than you can Bash.) Always part of a mixed pack of three mobs. The best strategy I've found is to just toss everything you have at them, trying to stay alive and ignoring everything else, only using Bash on a heal if you know you can kill it before it breaks out of the stun (20% or below, for me). Expect to die after killing it, corpserun, clear the rest of the pack.

Three-mob packs are random in composition, and therefore vary wildly in difficulty.

Anything with an Underbat in it is generally easier than one without, as the Underbat can be Hibernated and (temporarily) taken out of the equation.

Anything with an Underbog Shambler in it is generally very difficult to get down. Expect to die. I only ever clear packs with a Shambler if they're in the way of the chest in the corner (an extra Sanguine Hibiscus just isn't worth the repair costs; the chest is).

Anything with two Underbog Shamblers in it is impossible. They'll just chain-heal each other. Don't even think about it.

A pack with two Lurkers and one Shambler is extremely hard as well. If you try and kill the Lurkers, the Shambler will just keep healing them; if you try and kill the Shambler, it will just keep healing itself and the enraged Lurkers will tear you to pieces.

In general, you want to keep up Demoralizing Roar and Feral Faerie Fire on the mobs, to maximize the damage you are doing to them and minimize the damage they are doing to you. Hibernate should be used whenever possible, but not at the expense of being stuck in caster form with an awake mob beating on you; heals over time (at the very least Regrowth) should be applied pre-pull, to give you a bit of extra advantage. Try to have Frenzied Regeneration always up when you're dealing with things that are hard to kill (anything but Underbats); stealth around picking more Sanguine Hibiscus while waiting out the cooldown if you have to - it'll typically take less time than corpserunning back.

As an additional note: jumping in the water can save your skin sometimes - mobs can't follow you there, will evade, and will eventually reset. Try and not swim too far out, though - the fish bite.

Killing mobs as well as picking nodes, I usually come out of every reset with 20+ Sanguine Hibiscus, some extra gold and drops, and I've had fun as opposed to being bored out of my skull. Sounds like a win/win situation to me.