Jim,
There is a lot to learn about VW TDIs before you buy if you're not already knowledgeable of them.
Many claim the '03 and earlier were the best because they were simple and durable like the 12 valve Cummins. The earlier automatic transmission models are reportedly somewhat fragile.
The '04 through '06 models are nice cars with lots of features but have the "pump duese" engines which, I think, were similar to our 24 valve Cummins engines but likely to wear out cam lobes. Some used models with around 100k miles may be afflicted with a worn camshaft and lifters but a rough idle may be a clue according to what I've read.
The '09 and later use a Bosch HPCR fuel system similar to our Cummins HPCR engines. If the hpcr fuel pump fails, for whatever reason, tiny metal flakes tend to damage fuel injectors and the contaminated fuel is recycled back into the fuel tank and fuel transfer pump if this happens. A very expensive repair according to website info.
I've read a lot of whining on VW websites about how terrible the HPCR cars are and how greedy and evil Volkswagen of America is for not replacing their engines, even out of warranty, or their cars in the event of a failure. The facts I've been able to find reported by some mature owners suggest only a 2% failure rate of HPCR engines and it is most often blamed on accidental refueling with gasoline or with contaminated diesel fuel. I don't know the cause myself.
I bought a used '09 Jetta Sportwagen with 59k miles and love it. Cold weather and longer warm up times reduce average mpg some but longer road trips will produce 40 to 42 mpg, never less than 38 mpg.
"myturbodiesel.com" is an excellent website for all things VW TDI including buyer's guides. Some good information can be found on TDI Club but participants seem to me to be a younger group with a "someone else is responsible for my problems" attitude in some cases. Jetta Junkie is another site.
I've always liked German cars. Have owned a lot of VW beetles when I was younger and bought an '86 Golf new as well as an '87 BMW 325. My wife drove a BMW from '92 through '05 and loved it.