benefit to a home user who doesn't do photo or video editing but occasionally performs video transcoding (example, transcoding a video obtained only to be playable on the Apple TV)?
Sounds like you don't need an i5/i7. The i3 is no slouch and something like Plex doesn't require a whole lot of power at all. I'd consider the cheap model and test it out. If it doesn't work, return it and get something better.
Keep in mind that going up to the i5 version doubles your storage. 128GB is really small even for average consumers.