I own a 2005 yellow Limited roadster with the automatic transmission. The differences betweem model years are slight, if any. I see no reason why you should prefer a 2007 or 2008 to a 2005 or 2006. I also can't understand why anyone would be willing to pay more money for a 2007 or 2008 than they would for an earlier car. I can understand paying a premium for low miles, however.

FYI, if you're lucky (as I was), you might be able to find a one owner 2005 that has the transferrable 7 year/70,000 mile drivetrain warranty. To me, that was a good reason to prefer a 2005. By the way, there isn't a 2004 roadster.