My mac mini is -> MC270xx/A 2.4GHz Intel Core 2 Duo/2 GB DDR3 SDRAM (PC3-8500)/320 GB HD/SuperDrive/GeForce 320M/AirPort & Bluetooth Built-in
That's a 2010, with the newer unibody design, so yes, there are fewer reasons to force that to sleep because it is pretty quiet and "green." If that's still the stock 320 gig drive it's 5400rpm. I'm pretty confident you can run that headless Mini with no keyboard or mouse connected, screen share in when needed, have iTunes home sharing turned on, do Time Machine, have a printer on your network AND still expect that Mac to wake and sleep properly, because I do all of those things with several Macs in the house, including a 2011 Mini. So if it is worth it to you time wise you can eventually successfully troubleshoot this. (By the way, did you ever investigate whether it was your Roomie Remote discovery that somehow kept waking your Mini...)
But, that said, I also purposely keep a 2011 Mac Mini running 24/7, because keeping it awake and wired over gigabit makes everything else in the house more reliable in terms of media sharing: there's no trouble with any Apple TV or Mac in the house not finding my iTunes library and when I open the Air Video app on my iPad there's no delay seeing my whole media collection. I do let the various drives and enclosures and external volumes sleep, but the Mini that serves it all up, no. I'd suggest you live with it not sleeping for a while, doing everything
you want it to do and see if you come to value that reliability more than the few extra bucks it'll costs over the course of the year.