I had almost the exact same choice to make...I went with the new 2010 and decided to save the $1200. As far as i can tell, the only thing i'm missing is the kick start; at some point in 2010 they added a more convienient oil filter cap and updated some of the wiring harnesses, but my 2010 has both of the updates, (the factory doesn't necessarily only update things every calander year model, but appears to make changes throughout a year). Also, either way, you'll get the 2 year warranty.
Anyway, so far I'm happy with my choice, and with the $1200 i saved, i'm able to justify getting other odd's and ends for the bike that I wanted, (exhaust, larger headlight, bar-end mirrors, ect.).
All that being said, I do miss not having a kicker, but for $1200 i just couldnt justify going with the 2012 if that was going to be the only difference.
I'm sure other guys on the forum can offer other insight into the differences between the years, but I think the 3 I mentioned are the big three, and depending on when in 2010 it came out of the factory, the C5 you're looking at may have 2 of the 3 updates.
Either way, i'm sure you'll love it...I've had mine for just under 2 months, and after 1500 miles, I'm loving it.