Regardless that it doesn't have great long term potential, I've decided next to make a version of my Facebook app Your Japanese Name for iPhone / iPod Touch. The FB version has over half a million installs, although recently usage has gone to a mere 1600 monthly users. This was because I was unsuccessful at quickly converting it from a profile-based app to a feed-based one, although I did eventually do so.
There are already some similar apps in the App Store, but I believe I can get some installs if I can leverage the FB userbase. If I still have the list of user IDs stored somewhere, I should be able to inform users of the iOS version through a notification and get some installs that way. Since the App Store likely shows more popular apps first, it should push my version to the top, where it would then remain as it would enjoy extra installs from being the first listed app.
If this takes a week to make and starts doing $1 / day in profit, I wouldn't think it was a waste of time. Looking at this list of iphone app sales it seems possible.