I would pick my app carefully. Things that are specific to desktops like AV, disk cleaners, performance monitors would have staying power. Also word processors for specific constituencies. Scriviner, for instance, is for serious writers and is still supported by its creator. Diagram creators, slide presentation creators, even a database with an easy to use interface would be popular. I personally would love to see an…
About all I can say to sum up is, yes, pick your app carefully, but solve a problem you've researched and haven't found an easy solution to, and then ... see if you can build that into a business? :) It'd also be fun to build a meta-app: e.g. gamify learning about OS X, such as the activity monitor. Maybe it could be social, where you get points for being the first to get something set up amongst friends on the same wifi? That sounds like an incredibly niche market though...