Don't be concerned about being the 3rd owner of something. you still have the warranty so no problem at all. The 2009 model was a very good year. They started to but leds on the turn signals and they fixed the fiew issues they had with the 2008 models (chain and fuel pump), which were fixed under warranty anyway.
Except from doing some offroad stuff I don't see how the rims could bend so don't worry much about that. If it has a centerstand you can always make the wheels turn to see if you notice some change.
Soon somebody will suggest you the F658 Twin for your little commuting and your little offroad that is planned. It's a great alternative but chose the one that will make you smile everytime you look at it and the one you'll be able to put a great deal on :o). Since you're buying the bike from a BMW dealer there shouldn't be any problems. When they get a new bike they check it before selling it.
I bought a 2010 model last summer, and like you I'm not the first owner but it is still under warranty until 2013. It had 6000kms on it when I bought it back in june and now it has 21000kms. I love it and never looked back.
And to be honest I searched for month for a 2009 model because I wanted everything the 2010 had but in a yellow color scheme :o)
let us know how it turns out and welcome to the asylum!
Loutre - Tom
Keep the smile on your face!
F800GS - The ORANGE ones are faster!!