1. The vogue towards learning to fix the things you've bought might be an extension of upper-class appropriations of lower-class necessities as markers of authenticity. For example: smoking. There are two classes of people who still smoke: the working class, for whom they serve the same appetite-suppressing and energy-giving purpose as always, and those for whom cigarettes are a good affectation because it allows you to seem cool and buy or acquire nifty accessories. There's a line of criticism that affecting the habits of the working class for these purposes is a kind of mocking--witness that AV Club Hatesong article on "Thrift Shop", the gist of which being "there are people who have to buy their actual clothes from thrift shops, what gives you the right to be a dick about the stuff there?"--affectation to give perceived credibility, and so fundamentally unserious. The person who fixes because buying's not an option and the person who fixes because it seems like it'd be cool to do and if it goes badly you can just get a replacement are fundamentally different, and the latter doesn't bring about the ethos of the fixer but rather the dabbler. And there's nothing wrong with being a dabbler! But it's still different.
1bis. see also Pulp's "Common People".
2. I believe I saw this attributed to James Poulos on twitter, and so will at least provisionally give him credit for the idea: it's also possible that the purpose of hipsterdom, of which fixing is a part, is a generational response to declining standards of living. We may well end up making less than our parents. Rather than living an unsustainable lifestyle, we switch to inefficient but sustainable behaviors. Fixing et al still get an unjustified cachet, but get it as a means of softening the economic blow.