Some thoughts that have not been addressed-
The 2009 Cayman S has 320 bhp now, not that it was ever really underpowered, but now it's better.
The ride harshness issues (not really that harsh) can be improved by getting the "PASM" option. It's a driver adjustable suspension, whereby you can soften or stiften the suspension for your tastes.
Gas milage is comparable to all this category of cars.
The LSD option MAY be available now for manual cars, I found one in an inventory but did not call to confirm it exists. FOR SURE you can get a factory LSD with the new PDK trans right now. The are saying later in the year for LSD on the 6mt either way.
Buy what makes you happy behind the wheel. I was about $1,000 away from putting a deal toghether on a Cayman S when I bought my 135i. That was the worst car day in my entire life. On paper the Cayman S just was not worth that much extra cash, on the road...it absolutely is. And that was before the added BHP and LSD was available.
Check these sites out-
http://www.planetporsche.net/index.php
rennlist.com
I haven't been on rennlist in many months, but planet porsche has an excellent Cayman section.