I'm surprised at the three disagree votes. Most of this seemed almost trivially true to me:

• Popular political issues are non-neglected and likely to be more intractable (people have psychological commitments to one side)
• The reputational cost you bear in terms of turning people off to high-marginal-impact issues by associating with their political enemies is great than the low maginal benefit to these popular issues 
• Make the trade-off yourself, but be aware of the costs

Seems like good advice/a solid foundation for thinking about this.

A minor personal concern I have is foreclosing a maybe-harder-to-achieve, but more valuable equilibrium: one where EAs are perceived as quite politically diverse and savvy in both sides of popular politics. 

Crucially, this vision depends on EAs engaging with political issues in non-EA fora and not trying to debate which political views are EA or aren't "EA" (or tolerated "within EA"). The former is likely to get EA ideas taken more seriously by a wider range of people à la Scott Alexander and Ezra Klein; the latter is likely to push people who were already engaged with EA ideas further towards their personal politics. 

It might help to provide a short summary of main points discussed in your post.