It seems to me that, especially for an LW audience, an important part of Part II should be an examination not only of whether to save for retirement, but of how much. And that's got to consider how much real benefit you get from any given amount of spending now. And the MMM and ERE guys aren't just advocating the lifestyles they do because they get a kick from spending less money (though I think that's part of it) but because they reckon the tradeoff of a less spendy lifestyle in exchange for an earlier and/or more comfortable retirement is a good one. You or your readers may well disagree, but it's a question as worth asking as "can I just use the Singularity as my retirement plan?" which I see you have in there.

MMM-level unspendiness is well within the range of lifestyles LW readers would (I think) be willing to consider. (It's easier if you have a fairly high income, and many LW readers either have or expect to have in the future; it's easier if you have a lower discount factor, which I think LW readers tend to; and there are LW participants who give away the majority of their income, which is surely harder for most people than saving it.)