One thing that occurs to me is that we can approach the word causes on two levels

Yes. I quite explicitly mean everything from two people getting together to get something good done, up. I see it as part of the continuum of getting things done that charities are on.

Another thing that may be a potential blocker is that lesswrong has been identified with the whole SIAI/singularity/transhumanism cluster.

How I tell other people about LW: "Started by transhumanists. So they have these weirdy bits, but it's very good stuff."

But I am not sure whether this community wants to downgrade certain topics in the interest of openning up to other related causes.

I don't see a need to actively reduce it. Let other stuff grow normally. (This post may produce useful suggestions in that direction.)