I don't think prices will level off just because of supply- demand. As diesel cars get more popular, more people will be looking for the used TDIs.
You can't predict the future though. Just buy what you like and pay what you can afford to. Supply of the new TDI will take a while to catch up with demand, so it doesn't look good.
I don't think I would ever pay much over MSRP...just look at another dealer and don't get the "ether" in your head when you are looking at new cars, even used cars, otherwise you won't be able to think straight.
Walk into the deal with the mindset that you are going to walk away. Think about it, if you meet someone on the street and act like you are ready to marry the person, unless you get ...umm are a lucky person, I don't think it will go well. But if you come off as someone with other options, you will do better for yourself.