I did the math a while back, and fully talented a boomkin druid can do roughly 225-250% MORE DPS and DPM than a nuking druid of another spec (let's assume resto). Meaning if you could do 500 DPS as a moonkin, you'd end up pulling around 150 DPS if not specced balance. What you are suggesting with the moonkin form would be to raise that up from 150 to maybe 155...I'm sorry but if a cat is supposed to be pulling on average similar DPS (which it is) on mobs with 20% armor reduction (which I believe 30% is the usual assumption for "average" armor)...a mob would have to have 75% damage reduction to make the cat DPS EQUAL the untalented caster DPS. In other words, you're suggesting an increase in DPS so slight in comparison to other talents, and the reason to "nuke" is fairly null and void. Oh, and it's armor you're thinking of, defense is completely different.
As far as mini tree of life goes...that doesn't really fit with the way a feral healer would play anyway. A feral or balance healer is going to rely on HT more, because lower ranks of healing spells help HT more than the HoTs, and HoTs get buffed in higher tiers of resto. As such, a mini-version of ToL, which would boost HoTs (otherwise it would just make the dreamstate build uber if you could go mini ToL and still get the healing effects on HoTs). So even though a feral can heal if gearred right, getting a feral to heal with the resto style will be very cumbersome.
Next point on both forms - including the mini version of the form would decrease the effectiveness of the talent for the form. In general, moonkin is a 5% increase in DPS for all casters in the party. However, if you could get 2% already, the talent decreases in effectiveness down to 3%. People wonder why they need dire moonkin form, when the talent could be spent in other places. Same with mini ToL...druids may skip a point in dire ToL if it only slightly helps in comparison.
As far as other classes being able to use all their trees...shadow priests dont heal as well as holy/disc priests, and holy priests dont DPS as well. Healadins cannot tank to save their lives, retadins will have issues healing or tanking, and protadins are not going to be good damage dealers or healers. Granted they can heal, but they lose the efficiency of a holy healer.
While yes hunters can use traps in all 3 specs, a survival hunter is the only spec that can reliably keep a target CC'd permanently. But the hunter playstyle doesn't change much. Let's talk instead of mages - a frost mage is going to be playing entirely differently than a fire mage. Frost mages in solo do a lot of crazy things to kite groups of mobs around, but in groups have to rely on frostbolt spam. Fire mages will just nuke down targets in both solo and group play, but will have a nice shot rotation set up. No fire mage in his right mind would frostbolt spam unless the target was immune to fire - the mage should be specced for the encounter anyway.
I guess my point is, if you want moonkin, put 31 points in balance. If you want ToL, put 41 points in resto. Otherwise, don't ***** with it, and don't whine about it.