Have you thought about replacing one of your HTPCs with a Roku and using the replaced HTPC as a Plex Server? Something to think about.
I think for most people, using a Roku is fine for them as you may need a beefier back-end if you use
multiple Roku devices, but the front-ends are far cheaper ($99 MSRP). However, I did say "most people", as I
do not like using a Roku for one reason: anime. I watch a good amount of subtitled anime, and the anime scene has gone far beyond what you're used to seeing in movies for subtitles -- even foreign movies. The big push was to use stylized subtitles (SSA), which allow you to have a lot more customization over position, coloring, etc. Now, instead of seeing a bunch of signs in Japanese, the fansubbers can translate those.
Well, that doesn't
translate too well over to PLEX, which will burn-in the subtitles when transcoding as most front-ends don't support MKV but rather MP4. MP4 doesn't support modular stream selection, which means the subtitles have to be burned in.
There's also a weird problem with one anime series in particular: One Piece. For some reason, you
cannot have the subtitles on. If you do, the video will lag behind the audio, and it's not an issue with processing power as my back-end is powered by an i5-4670k!
I've been rather tempted to build a fun HTPC solution for my kitchen recently, and I finally did it yesterday. It's a touch-based solution (23.6" touchscreen monitor) using Windows 8.1 Pro (WMC support) on an i3 Haswell NUC (mounted to the monitor). Man, I was psyched... until I realized that PLEX Metro has to transcode everything
... and normal Plex Home Theater doesn't support touch since it ignores the mouse.