I wouldn't even use spit if its dps was spread over a longer time. Even now it's not that good against the better players that use dispell on it or use potions when retreating.
It's only powerful against newer players.. they try running away, die, and spam on the forums "Game is brokenn!!!!!11111 this is uncountereable omg!" when there are tons of counters. :/ A 250g potion will make sure it doesn't kill you on retreat.
And spit is not much damage compared to the dps he can do. :/
Also, even at half damage, it'd still be nearly as good per point as uproot..
Uproot now =28DPS per skill point with it and uproot(7 skill points). 33dps at lvl 4. Spit is 44DPS per skill point if you keep it going on 2 buildings.. Spit simply shouldn't be building targetable. Bestial rage is good enough for destroying buildings. ~_~
Most of what you say is pretty sane, but this is just plain wrong. It's fine as it is. The only other reasonable way to stack it (if not additively) would be multiplicatively, for a total bonus of 58.7%.
What I said is multiplicative. I'll explain my formula.
2 - (1 * 0.80 * 0.85 * 0.85) = 1.422
What is being done is you have +20% attack speed, and then you're adding 15% to what is LEFT, then 15% what again is left.
Right now ATK speed stacks really really crazily. And ATK speed is better than +dmg because of crit chances and other procs. So the formula should be changed. 