Are there any programs such as XMBC that will integrate with streaming services? Whatever solution I try it based to be very simple for the rest of the technically challenged.
Short answer to the most elegant way to get the streaming services is via apps on a streamer box.
No matter what you do there will be compromises and tradeoffs, but my experience with my wife has been that if 1) streaming and 2) simplicity/ease of use across multiple users were your highest priorities, then moving a Mini running OS X into the living room to take the place of what you did with the aTV3 (or on an iPad) adds complication. It's also harder to support, i.e. it takes more of my time. I've found it a lot easier and much more seamless doing NF, Hulu, HBO, YouTube and Amazon Prime with an aTV 3 (and that's including the caveat of having to Airplay Amazon Prime to the aTV from an iOS device since Amazon is being stubborn.) There was a time when I tried to do things like NF, Amazon and EyeTV within a front end like Plex and XBMC, but all of those solutions were kludgy and unofficial, whenever NF or Amazon updated their drm or changed their website the functionality would break and you'd have to head over to the support forums to see how long a fix would take. Very tedious.
I guess my ultimate advice is to pursue this change and see how far you can go, but you may end up concluding that doing things within a browser from across the room sucks. And in that case, for streaming media, use apps on a streamer like an aTV3 or 4; for accessing and playing back your own vast media collection, use a front end like XMBC/Kodi (or Plex) on a Mini. I have over 30 TB of media, a decade plus of archived HDTV, a decade of ripped dvd and blurays, that's what I use XMBC for. And yet I keep the aTV because it is so much easier to leave the internet streaming to it.
Adding another aTV3 for the living room might make sense for you, it can be had very inexpensively or consider an aTV4 for the living room and use the Mini mainly as a media server--I've had the 4 since day one, overall it is fantastic, you'll enjoy the streaming services within apps that are officially supported, Airplaying Amazon Prime from an iOS device is still seamless, and with an app like Air Video (or Plex) you can officially and easily stream all your locally stored content, MakeMKV rips, video with subtitles, odd containers and codecs et al with no need to "hack" the Apple TV. Just keep the companion server app running on the Mini and you'll be fine. That is until MrMC is released on the aTV app store
when that's released I'll be switching from Air Video to it immediately. Among other things it'll have DVR support and won't require a server app running on a Mac.