I use a 2010 Mac Mini as my HTPC. It has the original Disk drive but I have upgraded memory to 4Gig. It works really well I mainly run a Plex server on it and hardly use the disk drive since all my media is on a NAS. I brought it new and it has always served as my HTPC and performs no different now than the day I installed it. It has seen all the osX upgrades.
This is a very capable machine. Make it you reinstall OS X so its fresh. If you really care about it, you could give it 8GB's of RAM, and an SSD will make even more of a difference. I recommend getting any parts for upgrading from Other World Computing.
My 2009 Mac mini has served me for 6 years. 4gb ram. I replaced disk with 480 gb ssd and 2tb 2.5" disk in an optibay recently. Which certainly boosted performance.