I don't know of anything that would make a difference except perhaps the difference between the wireless cards. The older Minis would have an 802.11g card in them and the newer ones would have 801.11n. If you're doing wireless streaming and have any problems with throughput because of the distances involved or physical barriers you might get better performance from the 802.11n card. The difference in the CPU shouldn't be a factor.
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If you're not in a hurry and want to save some money you should check out the refurbished Macs at the Apple online store.
Batches of Minis come up every week or two but when they're gone they disappear from the site. Yesterday there were some available for $420. They're usually a current model, or the previous one, and have the same warranty as new. Shipping is free.