IMO if you're going green mill, then you're NOT allowed to splash blue. It's only a challenge if you can do it without resorting to using a color that's already good at it, which means no blue and no black.
The elder already combos with the Guidance & Lodge, and gives you inf. mana. The Fall lets you split the Wurm, which gives you 3 very solid defenders(not to mention 15 life and 15 cards). The Wurm itself was better when I still had Feed the Pack in here, but still serves it's purpose aswell as being an Alt. win condition on it's own. The good thing about this deck is even if they do use thier own vial you can just keep milling them. True this deck is weak to mass sweepers but every deck has weaknesses, you can't stop everything. That's actually one of the main reasons for the Elixir, to get everything back. Plus the druids get most stuff out of atleast damage sweep range. I wanted to add Strength of the Tajuru but can't find room.
It is true that every deck has a weakness, but limiting as many as possible is always a good thing. I agree with what you are saying about the Wurm, but withouth the Momentous Fall he is really a waste especially with a well timed Oblivion Ring . I just think running Elderscale Wurm and dropping the Momentous Fall all together would be a better plan. Harmonize can quickly draw you 3 cards, without anything else dependent on that. The Elderscale wurm serves as better protection than worldspine wurm, especially if he is not dealt with. Regardless of what choices you make for your deck they are yours, I am just giving my opinion for what it is worth. I can't see any logical argument for Llanowar Elves to be played over Arbor Elf in a deck with 16 forests and enchaments that enhance them. The potential for Arbor elves is much greatuer than llanowar elves and the downside is small. I like your build all in all I would just make these changes but to each is own. Good luck.
I wasn't trying to argue Llanowar over Arbor (in fact the Arbor IS better here), just pointing out that I already had a combo that produces a ton of mana. As for the Elderscale, I like the Worldspine better because he keeps coming back. Also I already have him where as I don't know how much the other would cost me, or even if the local shop has them.