Whether rejuv boosts a rogue's dps by 1% or 2% isn't really the point. A healer's job in a raid isn't to give some extremely minor dps boost, or shamans would be shocking on CD. Assuming a base of 14 points in balance and maxed-out Living seed and GoteM, it's a choice between having a workable HT via Naturalist and Emp touch or replenish. Personally I prefer boosting my main role in a raid and seeing as replenish is so narrow, I'm going to skip it.
The element of this talent that seems to be overlooked is that it doesn't remove the healing component of rejuvenation. If Rejuvenation is just increasing a rogue's dps by 1%, then it is probably a waste of ~5% of your actions during a fight (1 sec GCD/18 second duration). However it's also providing some fairly solid healing during that time as well. In any fight that features damage on rogues or other resource limited classes, Rejuvenation allows you to both provide the necessary healing *and* facilitate that class in performing their job.
Unless there's something I'm missing, it has a chance to proc off each tick - if a target is at full health, then it shouldn't give the Replenish effect. Also, it only has a 15% chance to proc. You could see a bunch of procs or no procs at all.
If the raid is taking damage, it's likely that we'll be using Wild Growth. If a single target is taking damage, they'd best be a tank (in which case the Rage and Energy components are useless, though the 1% mana could be useful on a Pally/Mage/Lock tank...maybe...when was the last time you saw a tank Rage starved?). If they aren't a tank and taking spike damage, then we're probably going to NS+Swiftmend them rather then let Rejuv run its course.
Unless I'm totally misunderstanding something, I just can't see this talent being useful in the slightest.
In all honesty, I think that quite literally every little bit helps. Any amount of rage that you're giving the tank while healing them is an amazing boon. Mana/Runic Power/Energy given while casting a healing spell that you cast normally anyway?
I really don't understand where the debate is. I believe it is completely worth the three talent points.