I think most humans' volition does include concern for animals, and a CEV AI of the kind MIRI wants to eventually create would be an astronomically good thing. It would probably turn the light cone into computronium full of blissful posthumans, wiping out most if not all darwinian nature it ran into, just because you can tile the universe more densely with people if you put them in computers. Posthumans would be much more computationally expensive than the simplest minds capable of happiness, so they would be packed much less densely and there would be much less happiness than a utilitronium future, but still quite a lot of it.
Spreading memes for people to care about animals does indeed have the potential to be a very good thing, especially because it's potentially useful in all of the futures where humanity decides what happens, not just ones where AI is the biggest existential risk (or close to the biggest). But if you are donating small amounts of money relative to the money already going into a certain effort though, each dollar is probably roughly as effective as the last, so a small advantage in the effectiveness of one effort over another means that that effort is the only one you should be donating to. Unless you are very rich, you probably don't want to donate some money to one cause, and some to another.
And as it stands, I think something like paperclipping is the most likely future, though.
I notice that a large fraction of Effective Altruism people are vegetarian. This makes sense: in general Effective Altruists take moral issues seriously, even when that means changing your lifestyle. I'm not sure it's a good balance, though.
One way to think about this is to convert it into money. How much would I need to be paid to give up eating meat? All animal products? How much money would I need to spend on myself to be about as happy as I would be with less money but continuing to eat animals? I'd probably be willing to go vegetarian for about $500/year, vegan for maybe $2000/year.
It turns out you can probably pay to convince other people to be vegetarian much more cheaply than that. I estimate the cost of a vegetarian-year at $4.29 to $536 while Brian Tomasik estimates $11 with better methodology (which I looked at). This is by placing ads on facebook for a site where people can watch an animial cruelty video and ideally become vegetarian or vegan.
If you would get more than $11/year worth of enjoyment out of continuing to eat meat, why not give $11/year to convince someone else to not eat meat for you? Or give $50/year and be on the safe side?
(While you're giving money, you should probably give it to the organization that you think will do the most good with it, which I think is probably one of GiveWell's top charities. The nice thing about money as opposed to actions is that it's easy to redirect.)
I also posted this on my blog.