In my opinion...a '06 COUP with 70,000 miles in good condition would be worth about $5000. A Roadster (convertible) with same miles might be $7000. The '04 (with lower miles) 33,000 miles would only increase the value by about $1000. Auto or manual transmission doesn't really effect pricing. Some may prefer one over the other but I don't think it effects pricing. This is just my opinion.