Some of the biggest features of the 2010 Mac mini are the lack of a fan, a much better power supply (internal, instead of a brick), and the ability to shift to 64 mode instead of 32. Also it's much easier to get into the thing to increase memory. SW tweaks, such as those Eric Hider suggests in the setup of the Tranquility, are also easily accomplished.
Carefully consider your peripheral HD. I've not regretted following Eric's advice regarding the Oyen MiniPro 2.5" FireWire 800/400, USB Portable Hard Drive using the Mini USB bus to power the HD. Small, silent, fast.
:) listening,
Ed