I've had two TD6's in the past four years, the first was a 02 reg Vogue bought in 2008 and wasn't a scrap of bother for the 12 months I owned it but I started to hear of them breaking and my wallet got scared so I sold it for a tidy profit.
I had a couple of other cars and then bought a 2003 model HSE in 2010 because I missed the luxury motoring of my first but WHAT a mistake! They are beautiful cars when running properly but I spent nearly £5k in six months keeping it on the road, with airbag suspension faults, compressor failures, injector problems etc.
I always vowed that I would only ever buy another one if it was less than 3 years old and still in warranty. I know that you have already mentioned the X5 and probably ruled it out, but my father in law bought a facelift 2006 3.0d sport recently for around your budget and its a fantastic motor, good perfromance and economy for the size (35mpg) but like any luxury brand, could still be big bucks as/when it breaks.
Can't really comment on the VW other than you don't hear as many horror stories
Are the 3.0 tdi touraegs still fetching good money then? You're right to ignore the 2.5 version, woefully underpowered.